I would rather sit alone in truth than with a million friends in fiction.

I don't think we need to disengage in debate with everyone. That said, you have to know if you're talking to someone who's willing to reason, and you have to be open to their reasoning as well. There is absolutely no sense in contradicting the opinion of an irrational person who has made their beliefs part of their core identity. That person will hate you for showing them the truth, no matter how clear.