Only a few years ago there was a great awakening of the human mind. Men began to inquire by what right a crowned robber made them work for him? The man who asked this question was called a traitor. Others asked by what right does a robed hypocrite rule my thought? Such men were called infidels. The priest said, and the king said, where is this spirit of investigation to stop? They said then and they say now, that it is dangerous for man to be free. I deny it. Out on the intellectual sea there is room enough for every sail. In the intellectual air there is space enough for every wing.
The man who does not do his own thinking is a slave, and is a traitor to himself and to his fellow-men.

The Liberty of Man, Woman and Child (1877)