Certainty is not biologically possible. We must learn (and teach our children) to tolerate the unpleasantness of uncertainty. Science has given us the language and tools of probabilities. We have methods for analyzing and ranking opinion according to their likelihood of correctness. That is enough.
Even Martin Luther and John Calvin believed that the Roman Catholic church, up to the Council of Trent, was basically orthodox - a true church with sound fundamental doctrines as well as significant error.