[Apologies for the l33t sp33k, but the lameness filter is actually pretty effective at blocking even the discussion of the older common tr0lls.]
Tr0lling originally started out as posting something on-topic but factually wrong in order to get reactions from people. Tr0lling was elevated by some to become its own art form; the best tr0lls could get pedants to crawl out of the woodwork like termites fleeing a flood. And the resulting posts and reactions were genuinely funny -- anyone who understood what was going on got a good laugh. But that kind of tr0lling peaked over a decade ago.
Other garbage has since cycled through Slashdot like ugly fashions on a New York runway. First came the memes: sites confirming the passing of various operating systems, etc., which at least often tried to stay on topic. They were inoffensive, but showed little real effort; they quickly stopped being amusing. Then came the nonsensical randomness, such as a certain movie starlet known for Star Wars and a lap full of hot breakfast food (I never quite understood that one). They were perhaps attempting to be absurd but mostly came off as stupid; again, they were reasonably inoffensive. But the current rash of copy-paste has become the new nadir, where cud-chewing morons too stupid to create their own original racism have figured out enough of the clipboard to re-vomit someone else's puke in the comments.
( In a huge burst of irony, some of the tr0lls themselves got pedantic, claiming the garbage posts did not qualify as "tr0lling" under their definition. Thus ended the reign of the major tr0lls, whose posts were quickly modded down into the -1 muck along with the rest of the bile. )
Throughout all of this, anonymous cowards and other low-lifes have always posted hate speech, political screeds, and offensive, racist crap. Browsing at -1, however briefly, will expose you to the words of horrible, useless human beings. Don't do it -- just click "no".
Slashdot has fought back, of course. The lameness filter has long kept out garbage like ASCII art, and certain phrases that I couldn't quote in this post. The remarkable bottom line is that Slashdot's moderation system, flawed as it may be, has kept the comments mostly readable for a very long time. Sites that failed to emulate it have come and gone, mostly forgotten by all but the Wayback Machine. Sites that still allow comments have almost nothing usable in them (youtube is a prime example of a site with unusable comments.) Meanwhile, Slashdot's community has managed to keep some semblance of order together. That's quite an achievement, especially over the nearly two decades of its existence.