I know well the feeling when someone challenges you on your beliefs and asks you to back it up with facts. If you don't have tangible evidence for that belief, the instinct is to get defensive and say that the person is being unreasonable. Being on the receiving end of that challenge often feels like you're being treated mean or unfairly.
Once you get over that emotional reaction and examine the challenge objectively, you realize it's not that big of a drama and in fact you might be wrong.
I've been on the receiving end of Viv's blistering demands for proof and facts. It wasn't fun. But then I realized it wasn't fun only because I didn't have proof and facts to back up what I was saying. Something clicked, and I realized I needed to have evidence before I went around spouting beliefs willy nilly, otherwise I just look silly.