The only thing more dangerous than an idea is a belief. And by dangerous I don't mean thought-provoking. I mean: might get people killed.

Nothing is more dangerous than an idea when it is the only one you have.

An idea that is not dangerous is unworthy of being called an idea at all.” — Oscar Wilde, writer and poet

There’s nothing more dangerous than a good idea.

Dangerous is a people's voice charged with wrath.

The only thing more dangerous than an idea is a belief.

Ideas are dangerous, but the man to whom they are least dangerous is the man of ideas. He is acquainted with ideas, and moves among them like a lion-tamer. Ideas are dangerous, but the man to whom they are most dangerous is the man of no ideas. The man of no ideas will find the first idea fly to his head like wine to the head of a teetotaller. It is a common error, I think, among the Radical idealists of my own party and period to suggest that financiers and business men are a danger to the empire because they are so sordid or so materialistic. The truth is that financiers and business men are a danger to the empire because they can be sentimental about any sentiment, and idealistic about any ideal, any ideal that they find lying about, just as a boy who has not known much of women is apt too easily to take a woman for the woman, so these practical men, unaccustomed to causes, are always inclined to think that if a thing is proved to be an ideal it is proved to be the ideal.

History itself is the only arbiter of "dangerous thoughts" and to whom they are dangerous. For the world does move. Men's thoughts change as the times change. You can no more freeze the thoughts of mankind than you can stop the earth from moving on its axis, than you can freeze a lovely face into eternal youth. To try to do this is not only to make a mockery of democracy, it is to stop the movement of progress and to whip up a fierce tide of reaction. Who should have the right to determine that another man's thoughts are "dangerous"? ("Jailed for her Thoughts")

Once you've got — actually got — an idea that is whirring around so fast that no other light or contrary evidence can come in, I think it's very dangerous.

No weapon is as dangerous as an idea. A weapon will kill you in that moment. A bad idea can kill you for a lifetime.

[A] theory is a very dangerous thing to have.

Thoughts are dangerous, he told himself, and thoughts against all science, all sanity, all civilized intelligence, are the most dangerous of all.

If ideas are "dangerous" then I am "dangerous" because I have ideas. I have ideas for a new system of government and society. Those ideas I have are called socialism. Socialism – a system where there will no longer exist a basis for the exploitation of man by man; a system of government where people – all people, without reservation – will be able to grow and develop into full human beings, where love will replace hate, where men, all men, can develop to their fullest potential.

An idea that is not dangerous is unworthy of being called an idea at all.