Too many wise things have been said for me to pick one as superior to all others. But here are some goodies from Emma Goldman:

"It is safe to say that no other superstition is so detrimental to growth, so enervating and paralyzing to the minds and hearts of the people, as the superstition of Morality."

"It is essential that we realize once and for all that man is much more of a sex creature than a moral creature. The former is inherent, the other is grafted on."

"All wars are wars among thieves who are too cowardly to fight and therefore induce the young manhood of the whole world to do the fighting for them."