Avoid foolish opinions.

“The most savage controversies are those about matters as to which there is no good evidence either way. Persecution is used in theology, not in arithmetic, because in arithmetic there is knowledge, but in theology there is only opinion. So whenever you find yourself getting angry about a difference of opinion, be on your guard; you will probably find, on examination, that your belief is going beyond what the evidence warrants.”

That’s Bertrand Russell, On Avoiding Foolish Opinions.

I found it on Farnum Street’s Brain Food.