I appeal to the philosophers of all countries to unite and never again mention Heidegger or talk to another philosopher who defends Heidegger. This m… - Karl Popper

All political parties have some sort of ‘vested interest’ in their opponent’s unpopular moves. They live by them and are therefore liable to dwell upon, to emphasize, and even to look forward to them. They may even encourage the political mistakes of their opponents as long as they can do so without becoming involved in the responsibility for them. This, together with Engels’ theory, has led some Marxist parties to look forward to the political moves made by their opponents against democracy. Instead of fighting such moves tooth and nail, they were pleased to tell their followers: ‘See what these people do. That is what they call democracy. That is what they call freedom and equality! Remember it when the day of reckoning comes.’ (An ambiguous phrase which may refer to election day or to the day of revolution.) This policy of letting one’s opponents expose themselves must, if extended to moves against democracy, lead to disaster. It is a policy of talking big and doing nothing in the face of real and increasing danger to democratic institutions. It is a policy of talking war and acting peace; and it taught the fascists the invaluable method of talking peace and acting war.

The so-called paradox of freedom is the argument that freedom in the sense of absence of any constraining control must lead to very great restraint, since it makes the bully free to enslave the meek. The idea is, in a slightly different form, and with very different tendency, clearly expressed in Plato. Less well known is the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them. — In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant. We should claim that any movement preaching intolerance places itself outside the law, and we should consider incitement to intolerance and persecution as criminal, in the same way as we should consider incitement to murder, or to kidnapping, or to the revival of the slave trade, as criminal.

If we are uncritical we shall always find what we want: we shall look for, and find, confirmations, and we shall look away from, and not see, whatever might be dangerous to our pet theories. In this way it is only too easy to obtain what appears to be overwhelming evidence in favor of a theory which, if approached critically, would have been refuted.