They often couch this sort of behavior in the idea that they are "straight shooters" or they they are "frank" or that they "don't suffer fools". Usually it means that they just don't have any tact or regard for others.
Most of us have let ourselves respond in ways that we shouldn't so I'm not throwing stones. Just saying.
And then there are the trolls. They are here (earth) to disrupt and insult.
In my experience this is a universal problem on earth that is magnified by the internet. Audiogon seems slightly worse than a lot of other sites I frequent. I don't know why.
I had to step away from Audiogon for a while for this reason (and my tendency to get drawn into the pig wrestling).
Now I try to avoid any threads about contentious subjects altogether.....except for this one.