Not that i am condoning this in any way, but it seems to me like the culprit here isnt UA, (or by extension AC) it's airport security. I can't help but think that forcibly removing someone from the airplane was a very bad solution but i can't figure out what else they could have done? Offer more money? Probably cheaper to them than what this will cost them in bad PR but once again all UA did was call security, not drag the poor guy. The dragging is on the security guys.
I'm puzzled that once this started happening no one just got up and said :" OK OK, i'll go just leave the poor guy alone. "