> Of course their friends who I don't know can also see my comment, and they quickly weigh in with their un-thought out vitriol. I try to keep the discussion going for a little while, but they quickly degenerate it into ad-hominem attacks (which is impressive because I am a stranger to them) and I give up.

Sounds similar to real life though when serious topics come up...some people aren't interested in their views being challenged, get overly defensive and don't care about what an ad-hominem attack is. You're best either avoiding those kinds of conversations or those kinds of people.