It's a sad part of Internet life but it's not easy to get away from the troll. Even on sites with registration, any one with half a brain cell can sign up perfectly respectably and then get on board and start antagonising all and sundry.
It's easier when the majority of the site contributors are of one mind or one desire. Go on to a conservative website and be a liberal, go on to a weather site where the vast majority of members are looking for cold and claim it's not going to snow and see how far you get.
I don't know whether individuals could derive some gratification from annoying people - I don't care thet much - but it's the price of free speech.
I don't envy those administrators who have to spend their time moderating forums and keeping the trolls at bay but that's also the price of free speech.
Unfortunately, the assumption is that free speech means unrestricted or unlimited speech. That may have been true once but perhaps we need to be moving toward a more modern concept of responsible speech where what you say and how you say it is as fundamental as the right to say it.