"[T]he growth of knowledge depends entirely on the existence of disagreement."
This, in itself, is an excellent quote. Yet, the full quote, taken from The Myth of the Framework, is even better:
I hold that orthodoxy is the death of knowledge, since the growth of knowledge depends entirely on the existence of disagreement. Admittedly, disagreement may lead to strife, and even to violence. And this, I think, is very bad indeed, for I abhor violence. Yet disagreement may also lead to discussion, to argument and to mutual criticism. And these, I think, are of paramount importance, I suggest that the greatest step towards a better and more peaceful world was taken when the war of swords was first supported, and later sometimes even replaced, by a war of words.If one did not know better, one might think Popper was speaking in defense of the Danish cartoons which sparked riots around the Middle East.