I agree with the OP, that rudeness is a problem. I have been on Audiogon for over 20 years and personally, I don't feel it is getting worse. This site is by no means the worst, some UK forums are positively incendiary and we are supposed to be exemplars of good manners.
I think if you offer your opinions as opinions, not facts everyone should agree with, then you rarely get sniped at. I can only remember one instance, where I suggested I wasn't a Magico speaker fan, after several long auditions at shows. The gist of the response was that I had no right to offer an opinion unless I'd had a long audition in the home, which is plain stupid.
So if you offer an opinion, expressed as an opinion, you don't abuse other users and stick to the thread, not hijack it, I don't think you should have or deserve, abuse.
Anyway, who gives a c--- what ill mannered people think about you, life's too short to give a dam