Well, for some perspective I offer three older posts that addressed a different issue but tend to apply.
Once a person has convinced him or herself that s/he is correct, or has a pretty good take on the world, the notion that s/he is a sap, fool, tool of advertising, subject to the laws of behavioral conditioning, biased, mistaken, illogical and the like is outside of the Overton window. Consequently, anything that suggests to them that they are mistaken, etc, must be flawed, illogical, unfair, below-the-belt, not-cricket, uninformed and/or meaniepants.
This is when it is occasionally necessary to call someone a nasty name and attack their person, as opposed to their argument.
Okay, okay, calm down knickers-knotters and sphincter-ratcheters. We are not talking about the tactics of a specific venue and whether it is in fact better to call someone an asshat straight out (dorm room bullshit session, pub, etc) or elocute around it semi-politely in such a way as they know exactly what you mean. I still maintain that tactically the best approach is to address the act, rather than the person but I allow for exceptions. Nevertheless you need to make some things explicitly clear.
You do not agree that the two of you are on the same side, that you are working for the same goods and that this person is one of the good guys. Rather, you believe that this person is on the bad side and in your estimation closer to the people you both agree are on the bad side, than s/he is to the people you both agree are on the good side of an argument.
So why get in these fights? Is it a moral flaw? Some might see it that way. A bullying personality? Perhaps, although I'll return to this in a minute. A variance in entertainment preference (sure) similar to those who enjoy boxing, hockey or dogfights (ummm....)? Blowing off steam? Cry in the wilderness? Staking a claim? Street theater?
Happy reading. Make sure to check out the comments from my always perspicacious readers.