I always try to give myself some time before responding to a comment that upsets me. I let the inital emotion subside and then think of some polite way to offer up logical counterarguments. As long as you keep things civil, you'll always encourage conversation. If you just spout something back, then you're asking for a reduced level of discourse.

And yes, it drives me crazy when the conversation strays from my original topic, especially when it appears someone's missed the point of my post. But, I suppose I should learn to let go of that. Your other readers are right -- we can learn a lot from the strayed conversations.

The thing that bothers me most about the social media bashing is that the loudest voices in that seem to be from the people who haven't even tried to understand the good in it. I get why people who don't use it see the narcissism, but like you said, that exists in real life (and I think anyone who pretends they aren't just a smidge narcissistic would be lying). But I've had so much good come from social media in my life: It helped me build real-life relationships when I moved to a new city, and those friends are my closest friends now; I met my current boyfriend through blogging; I've discovered neat places and history about my current city that I wouldn't know of otherwise; my blogging friends helped me survive a bad breakup;  I've discovered more about who I really am and what I want from life ... I could go on.

I guess what I'm saying is, don't knock it 'til you've tried it!