I agree with cofty. I've grown a lot over the years from conversations with people who challenge what I believe or what I am doing. It's not comfortable, and sometimes my feelings are hurt, but in the long run I grow from these challenges. I've done writing for pay, too, and non-fiction writers are regularly challenged by editors. We have to justify what we say with evidence, we can't just say things we were taught or heard and think might be true. Nothing wrong with being challenged to defend your beliefs, although I don't challenge people unless they shove their beliefs in my face.
Cofty isn't mean or nasty. He's just completely frank and honest. It's hard to take if you're used to mealy-mouthed people. I like the brutally honest, in fact, as long as they don't think being honest means being vicious.