Nice one Bob. I have had my periods of closed-mindedness on certain subjects. I was very closed-minded when it came to politics for a few years - anything other than anarcho-capitalism, I wouldn't give it a fair shake, and I'd dive into arguments.

On the whole though, I've only become more open-minded as time goes on. I do see people in Internet discussions saying things like "Oh okay... you're going to question whether Sandy Hook happened like they said in the news. I'm out." Or "You're going to question whether gravity exists... I'm out." I can't say exactly what they're feeling in that moment, I guess it's just cognitive dissonance, fear, general discomfort. When you start asking certain questions, they just don't want to hear any more.

Personally, I love hearing questions I've never heard before, doubting things I've never doubted before.

People are generally very uncomfortable with uncertainty, probably a consequence of government schooling. Nothing can be an open question, it has to be black or white, and they need to know what it is now. But life is a perpetual mystery, we'll never know exactly what we're experiencing, if we'll wake up tomorrow to find it was all a dream. For many, that idea is scary... it is for me too, but it's also exciting.

So basically, I don't know where my line is. I'm sure for many there's also an associated blind spot, so maybe I've blocked it out.