I often heard so many misbeliefs about Esperanto, from people who know absolutely nothing about the language. Sadly, those who spread those rumors are often well educated people.
The common mistakes are:
What is the reason for those people to do that? Does it have any psychological roots? Do we have any investigations on that?
Claude Piron, a very famous Esperantist, wrote an essay about this very topic. He provides the following “underlying anxieties” under some people’s uneducated attacks against Esperanto:
Most if not all of the criticisms that arise from these are not based on actual facts about the language. I highly recommend reading the essay.
The explanation seems quite simple to me. The natural line of thought is: if Esperanto was a good idea, people would have adopted it; but people haven't adopted it, so it wasn't a good idea, and I won't bother investigating further. If I am a teacher or an authority figure and somebody asks me about it, I can just say something plausible-sounding and leave it at that.
Remember that for adults, learning languages is hard. Esperanto is already perceived to start with as "Utopian", which is a code word for "a nuisance". Accepting the validity of the Esperanto idea would mean accepting the task of learning a new language. How many busy people would want to do that if they could find, or invent, a reason not to? No major power sees a reason to promote Esperanto when they could promote their primary ethnic language instead. And many ambitious people from smaller countries have worked hard to learn English; why would they be eager to remove their own advantage and start again from zero? So, for most adults, and especially adults in a position of power, there is a strong initial impulse to push the idea away. This means that as long as Esperanto is marginal, the myths will tend to stick around.
In some cases there is psychological resistance to the idea of Esperanto, as Claude Piron pointed out. But in other cases, people just have assumptions, and their assumptions seem so obvious to them that it doesn't even occur to them that they could be incorrect, so they never even think of researching it.
When I talk to people about Esperanto, a lot of them have never heard of it, so when I try to explain what it is, I see this first-hand. If you say that it's a constructed/invented/artificial language, whichever term you use, that translates in people's minds as "made-up language". And if it's a "made-up language", than of course (in their minds) it
As Arika Okrent observed:
They [the invented language books in the library] were testaments not to the wonder of nature but to the human impulse to master nature. They were deliberate, painstakingly crafted attempts to tame language by making it more orderly, more rational, less burdened with inconsistencies and irregularities. There were hundreds of them. And they were all failures, dead in the water, spoken by no one.
Well, of course they were. If you plant a plastic flower, will it grow? So I was skeptical about the claims that Klingon -- Klingon? -- had really defied the odds and sprouted roots.
-In the Land of Invented Languages by Arika Okrent, pg. 6-7
But the difference between Klingon and Esperanto is that they've heard of Klingon (at least here in the US), and haven't heard of Esperanto, so the obvious conclusion is that there must be more Klingon speakers than Esperanto speakers.
I myself, when I read about Esperanto, assumed that it was a fringy made-up language that nobody speaks, but I was too excited about its lack of irregular verbs and plurals to care. So I went ahead and learned it, and through learning it came to know better. Not everybody cares enough about it (one can't care about everything!) to bother doing that.
At first a small comment: Please have a look on "The Debunking Handbook" on skepticalscience dot com. They think you should never quote a misinformation without mentioning the truth before and after it, just to avoid that the misinformation continues to spread. I tried to apply this in Facts and errors about Esperanto (the numbers, e. g. Duolingo, are from last year).
You wrote: "I often heard so many misbeliefs about Esperanto, from people who know absolutely nothing about the language." No. I would be glad, if they knew absolutely nothing about Esperanto - but in fact they have a solid half knowledge. Quite often they know a lot about the language itself, about grammar, word derivation... This impresses the public, which is then ready to accept also the nonsense about Esperanto, the false idea, that nobody would speak the language... (while in fact probably some hundred thousand use the language on a regular basis).
It seems to me there are a lot of reasons why there is so much misinformation about Esperanto. I will deal mainly with the idea that (nearly) no one speaks Esperanto, as this is the basis for other misperceptions: If (nearly) no one speaks Esperanto, then it is clear that there are no books in Esperanto (no writers, no readers). If there are no books, then there is no culture. Such a language is called "dead". And it is clear that any number of Klingon speakers is higher than zero...
By the way, I think, it is helpful to inform the public with some numbers. Someone who hears about 120 new Esperanto books a year won't continue to think that 'nearly no one' speaks Esperanto... Up to now about 10,000 Esperanto books appeared. It is very difficult to imagine a language community with less than 100,000 speakers, if there are about 120 published books year after year. We are discussing about a realistic number of Esperanto speakers for decades - but it is very difficult to discuss about the number of 135 Esperanto books (49+ pages), published in 2015, in the catalogue of the Universal Esperanto Association (about half of them are fiction books in Esperanto).
So, why is there so much misinformation about this language, mainly about the fact, that a lot of people speak Esperanto?
If you understand Esperanto as being an alternative to English as the main international language, then the perception of the spreading of English guides you to the false idea that Esperanto has been put aside. This sounds logical, but in reality English is far from being enough to communicate with all people worldwide. Even the best estimations mention only 1.5 billion people speaking English - so at least about 80 % of the world population don't speak English. If you want to speak with some of them, then you have to learn their language, or to learn a language they learnt. Nowadays Esperanto is (nearly) not in the run to be the first foreign language of anyone (not having English as native language), but to be one of the secondary or third languages. (Yes, there are people speaking more than one foreign language... :-) They form a major target group for Esperanto outside English speaking countries.)
Many linguists are paid for the education of English teachers. If there would be a shift from English to Esperanto - and this is one of the ideas linked with Esperanto -, many of them would lose their jobs. (Yes, in a very long run, but however, you never know...) So they are not very enthusiastic about such a perspective. We can imagine, they are ready to absorb any negative information about Esperanto with a lot of joy - and they do not like to hear positive information about Esperanto. So in a circle of linguists no one gets a lot of applause, if he or she tells the wonderful story of a little schoolboy some hundred years ago who managed to lay the basis for an international language which can be learnt in about a third of the time you need for English; and that language is still spreading around the world, amazing, no? :-) It's just about competition, no one is happy to hear of the progress of a rival - and a lot less, if this rival has some very obvious advantages over your own product, as in the case of Esperanto. So it's easy to understand that many linguistics textbooks do not mention Esperanto. Others just mention that it was an attempt to establish an international language, but, haha, "it failed". (Yes, quite often we find that - it should be: The attempt to become the first international language wasn't successful up to now, but the attempt to create a working international planned language with literature and songs and an own culture, spoken by people in more than 120 countries - that succeeded :) ) In general life we follow "Of the dead nothing but good is to be said" (de mortuis nihil nisi bene). For many linguists the slogan seems to be: "Of Esperanto nothing but bad is to be said".
Linguists worldwide are nowadays very much influenced by U.S. linguists. Some speak of a kind of colonial situation. (And you may want to reflect about the role language plays here.) This means, linguists worldwide tend to accept the views of U.S. linguists - and these (used to) live in a rather monolingual country. It's easy for them to assume that everyone speaks English at least to some degree. - As speakers of other languages live far away, there are only very few Esperanto speakers in the U.S.: There is about one member of the Universal Esperanto Association per one million of U.S. inhabitants. In Iceland there are about 70 members per million of inhabitants (well, 7 per 100,000), seventy times the proportion in the U.S. So it is very easy for U.S. linguists to get things wrong about Esperanto.
Things are a bit similar for language teachers, translators and interpreters. They just can't be very enthusiastic about Esperanto, a potential job killer - if they do not decide to learn it... So they are more open to bad news about Esperanto than to good news.
Some journalists studied languages - so some of them heard the misperceptions their university teachers had about Esperanto. A bit difficult to convince them that those cherished teachers told nonsense - and a lot more difficult to convince them, when you in fact do speak Esperanto. Because in the eyes of the public every Esperanto speaker is biased... (Mainly when he or she argues for a general introduction of Esperanto, but also when he or she just describes the current situation of the Esperanto language community.)
If there is an article about Esperanto which has misinformation, the journals are not happy to correct this, as they should following the "Code of Ethics" for journalists: "Gather, update and correct information throughout the life of a news story." But who really wants to say: "What we said about Esperanto, is complete nonsense." Not a wise marketing idea... So they avoid this like the plague and at the very best, there will be a comment of a reader.
The whole industry and the public education institutions in many countries accepted the fact that English is the main international language and they learned to live with this. They are not enthusiastic about change (as most people are not). So they are mainly just silent about Esperanto, they are not the ones who would be willing to correct misperceptions about the language. If public education institutions have to speak about it, they ask linguists - about them see above... For the results see for instance the French Government which told the parliament several times, that Esperanto would have no native speakers. An error, but why should they correct this misinformation?
Some people have argued that Esperanto isn't in the interest of the English speaking countries like Britain and the United States. Daniel Rothkopf wrote in 1997 that "it is in the economic and political interests of the United States to ensure that if the world is moving toward a common language, it be English". Others calculated that the annual turnover of the English language industry is well worth some billions (British Government, Robert Philippson, François Grin). Probably the institutions of English speaking countries are in favor of English, but not really of Esperanto. It is not publicly known what is done in this direction, but it would not be too surprising, if they tried to influence linguists the public opinion favouring misperceptions about Esperanto.
I hope that some of these ideas will help to understand the mechanisms of misinformation about Esperanto. It's certainly not an exhaustive list, as I did not speak about the role of Esperanto activists and associations (what do they say, what effect does it have?).
It's because of the homogeneity of disinformation over the entirety of the cognitive realm. The OP's question confers victimhood to Esperanto, and caters to the perspective of the users of this forum, but pernicious prejudices / fallacies / misconceptions abound across the board. To take just one example, the high regard that milk is held in is totally unwarranted. The fact is, human beings have no business drinking cow's milk. A renowned physician, Dr. Frank Oski, even wrote a book exposing and denouncing this misconception: DON'T DRINK YOUR MILK. Please don't obsess over this example. It is just one of many that could be given.
