The early Church was intolerant, like most religions. And it may be that the early Church only survived, because it was intolerant. But one might have expected religious sects to grow up a little with the increasing knowledge of the natural world. There are disadvantages in taking yourself and your creed too seriously, because the harsh yardstick for any faith is its fruit, that is how its adherents behave. Nowadays we tend to think of anyone who claims to be in possession of the whole truth, as demented; it is so obviously untrue. Unless some mathematical physicist thinks of a theory of all things, we have to accept that hitherto every scientific hypothesis has in due time been replaced by another one, which approximated more closely to the truth than the first one did. And it is difficult to see why it should be any different in the religious world, unless science is rejected, because in science it is not fashionable to claim that “your truth” is final. So either you need a split mind, which keeps religion and science is separate compartments, or you reject science and embrace a desire to return to the credulity of the Middle Ages. Neither alternative is an attractive proposition for someone with intelligence. And since I think that religious experience is indistinguishable from any other sort of experience, my opinion is that the same holds good for religions as for science, which is after all a religion for some people. If you think God speaks to you, that is an experience like any other.
But even if a group does not claim omniscience, but only that it possesses the one and only key to heaven, it is difficult to take their pretensions seriously. This is so, whether their key is in Biblical fundamentalism, or in the claim that evolution is limited to natural selection and survival of the fittest. Both claims seem to me absolutely absurd. Yet I would no more set about trying to prove that they were wrong, than claim that my theory of consciousness will never be overturned; because I may be wrong. Naturally I hope that further work will tend to confirm there is some truth in my theory; but that is as far as I would wish to go. Similarly with claims to hold the one key to heaven, I refuse to take them seriously. Those who claim to have the only key to heaven, in my opinion, are in effect making the mistake Antigone made in the old Greek play. It is a mistake that leads down the road to catastrophe. You cannot avoid the need to make judgements. You have to find out what works for you.
But can my sort of religion hold its own against the vehement, and even violent, faith or bigotry of others? Does “faith like a grain of mustard seed” remove mountains? No, in my experience it does not. And if it is objected that I probably did not have enough faith to remove any mountains, may I point out the whole point of the original exhortation was to suggest that you did not need very much faith. It may be true for some people; but not for me. And I am bound to add, that I do not know anybody for whom it is literally true; although I firmly believe that healing occurs from time to time in every age and in every community.