It is claimed that the Orwellian "newspeak" (in his novel Nineteen Eighty-Four) is created to mock at Esperanto. Why was George Orwell's attitude towards Esperanto so negative?
George Orwell doesn't appear to have hated Esperanto, though he seems to have feared the potential for abuse found in a universal language.
He was exposed to Esperanto through a friend of his aunt, Eugene Adam, who was, according to Robert Plank, "so enthusiastic about Esperanto that he did not willingly speak any other tongue." Plank continues:
There does not seem to be any hard evidence that Orwell himself learned to speak, read, or write Esperanto, but it is very likely. (George Orwell's Guide through Hell, 90)
Another proposed "international language" striving for prominence in the early 20th century was Basic English, and Orwell's criticisms of it seem likely to apply to Esperanto as well. Nadel and Buitenhuis write:
Although Orwell was interested in Basic, and although he thought that a universal medium of communication would be conducive to international peace, he was wary, as he says in his review of Hogben's Interglossa, of 'the sinister way in which several living languages are being used for imperialist purposes'. (George Orwell: A Reassessment, 103)
They quote John Atkins' analysis:
Perhaps the reason why his sympathy with Basic English never developed into overt support was because he feared that Basic might be the forerunner of the manipulative language that he illustrated in Nineteen Eighty-Four. (103)
It seems to be based on personal experience. Here are several links that give some background:
And [a]pparently, Orwell, during his down-and-out phase in Paris, had to accept a room in the lodgings of a cousin. The fact that she and her live-in lover spoke only Esperanto together at home — a language he could not understand — left him less than enthusiastic. In the same text there is also a claim (from the early 1980s) that Newspeak was actually a satire on Basic English, which he disliked for other reasons.