Where do we draw a line against the intolerance of bad ‘religions’, of which the philosopher regarded Nazism as a secular variant? Today, militant Islam fits that same mould — as do its left-liberal apologists, whose reverence for relativism is the offering laid before the altar of totalitarian militancy.
“I have insisted that we must be tolerant. But I also believe that this tolerance has its limits. We must not trust those anti-humanitarian religions which not only preach destruction but act accordingly. For if we tolerate them, then we become ourselves responsible for their deeds.” — Karl Popper
That comes from a lecture on science and religion, delivered in 1940 in New Zealand in a university extension course, Religion: Some Modern Problems and Developments. The lecture has been published in After the Open Society, edited by the ANU’s Jeremy Shearmur and Piers Norris Turner of Chapel Hill, North Carolina. A summary of the main ideas in the book can be found here.
Popper wanted to bring together people of good will, despite their differences. That was Hayek’s aim in The Road to Serfdom, which he addressed to the socialists of the world This does not mean glossing over differences or holding back from criticism of mistakes, but it does mean taking a stand on common ground when it exists. I think that Popper would be surprised and disappointed by the militant atheists. He was a secular humanist, however he argued that the dispute between religion and science in the 19th century was a thing of the past because it was based on each side intruding on the territory of the other. Science is concerned with the way the world works and it does not presume to answer questions about morality or the purpose of life. Religion is a rival for science when it tries to trespass on the territory of science to describe how the world works. The antagonism is intensified when each side thinks that it alone holds of the criteria to decide the issue with certainty.