Live And Let Live ? (Facebook-style…)

Recently, after replying to a friend’s Facebook posting, in which I very rationally and unemotionally explained my opposing viewpoint and explained the compassion upon which my reasoning is based, someone replied to my reply. The bulk of this person’s reply, diametrically opposed to my own very considered opinion, seemed thoroughly researched and well thought-out (minus a couple of non-sequiters and a some cognitive dissonance – But, hey, this is Facebook we’re talking about, and people on FB tend to write “on the fly” without proofreading or editing before pressing the “post” button. Maybe he/she was drunk or something, too. Who knows. No big deal.)
Had that person stopped at that, I actually would have consulted his/her cited references and statistics.
But he/she tacked-on a final paragraph, almost entirely ad hominem personal attacks against me, attacking not my argument, but my mindset, or rather, what this person projected to be “my” mindset, not knowing me, never having met me. His only knowledge of me was that dozen-or-so sentences I’d written . (Well, maybe he/she looked at my FB profile, too, which isn’t very much, and certainly doesn’t “let you inside my head”.)
Among the venomous accusations he/she hurled was that I show no compassion. I was tempted to reply, asking him/her what his/her definition of “compassion” is, and even began to respond, again very civilly, but thought again: By tacking-on his/her vicious little irrational adolescent tantrum to his/her otherwise-calm piece, he/she had simply discredited him-/herself, showing him-/herself to be unworthy of a response.
So I just replied “Oh” to be polite, although it was quite sarcastic at that point. But I guess that sarcasm doesn’t shine through a two-letter post on Facebook.
His/her response to that was on the order of “Yeah ‘oh’! See!” Again, quite adolescent. Civil discourse seems to hold little value to this person.
When someone attempts to FORCE their own viewpoint down your throat, to impose their own (generally myopic) viewpoint – their own “take” on reality – on you via a caustic attack, they’re bound to be resented and rejected, marginalized and trivialized. Didn’t this person learn that as a child?
(I’m tempted to inquire as to what event/events went wrong in this person’s childhood but it’s none of my business, I don’t even know this person, and unless he/she wants to friendlily argue over a pint-or-two of Guinness, I have a hunch that it’s just best to ignore him/her. He/she brought it on him-/herself.)