I left Slashdot for pretty much the same reason I left Wikipedia: A culture that tolerates incivility and rudeness, and a culture that is more interested in debate for debate's sake instead of accomplishing anything.
My last non-Anonymous post to Slashdot was in response to the following:
I take it you were dropped on your head as a small child.
And was as follows:
Just to let you know, I feel that comments like this are very inappropriate to say to anyone, either on-line or off-line. This is a very nasty personal insult; I have been to schools where this kind of language would not be allowed (it is "fighting language"; language which angers someone enough to start a fight in the real world).As a result, I have placed you on my foes list. If you wish to be taken off of my foes list, please apologize to the person you have personally insulted, and mail me proof that you have done so.
You are free to continue using this kind of language, of course, but people will respect you less and your karma will undoubtably suffer.
The result? The original very rude comment was moderated up as a good comment, and my comment was moderated down as being "offtopic". The message was clear: If you act like a jerk and attack someone, slashdot moderators will think you are being funny. If you tell someone they are being uncivil, slashdot moderators care so little about civility that they will moderare you down.
That was nearly three years ago and the last time that I ever posted non-Anonymously to Slashdot; while I did later post anonymously (with posts that got moderated up all the way to five from zero to boot), I stopped even posting anonymously once Sean pointed out Digg to me here on Myspace.
Life is too short to be involved in communities that not only tolerate, but downright encourage rudeness.