Can a language be dangerous?
Some think it can.
We see some of them just now, in North America among the most rabiate Obama-haters; those who are so far out at the extreme right-wing that they think George Soros is a leftist (which he definitively isn't when seen from a European perspective).
The say Soros has bought the Democratic party, and the soul of Obama, and since Soros' father was an active Esperantist (and the name "Soros" may be interpreted as an Esperanto word, meaning "will soar"), this is something that is held against him.
(Actually, Mr. Soros' links to Esperanto seem to be very weak nowadays; as far as I know, he hasn't given a single kopek to any Esperanto project.)
These Obama- and Soros-haters are not the first to see Esperanto as an abomination and a threat to humanity, or at least to their own power and ambitions.
Two of their most famous predecessors were Hitler and Stalin.
I have read a book about this: La danĝera lingvo ("The Dangerous Language"), written by Ulrich Lins in Esperanto and first published in 1973 by Omnibus, Kyoto, Japan; an extended version was published in 1988 by Bleicher in Germany, and still another in 1990 by Progreso in Moscow (where it finally was possible to publish this kind of books).
I don't know if there is an English translation in existence, or in planning, but the book has been translated into Japanese, German, Italian, Russian, and Lithuanian.
(Sometimes I am feeling sorry for you native Anglophones. The English language has a great original literature, but in the field of translations some less used languages are actually better off. That's a good reason for even you to study languages.)
The main departments of the book are:
1. Suspicions Towards a New Language (about the first decades of the Esperanto movement, e. g. the French battle against Esperanto in the League of Nations)
2. "Language of Jews and Communists" (about Nazi Germany and its occupied countries)
3. Persecutions in East Asia
4. "Language of Petite Bourgeoisie and Cosmopolitans" (about the Soviet Union, especially during the Stalin era)
After Stalin's death, I may add...por mori informazoni lir HubPages