I've done a fair bit of trolling in my time (Habbo, Youtube, Minecraft, etc.). I can honestly say that there is clearly no purpose to trolling other than to simply get a laugh out of people you don't know by pissing them off online. Sure, it isn't nice, but neither is schadenfreude in general. But having done it before, I will admit that it is fun. Trolling is a art and a hobby to most of us because it values subtlety over brute force, forethought before mindless action. I remember a Minecraft server in which I rather deviously wrecked their monster spawner using torches.
The author in the article mentions that many trolls would have trouble with "meatspace" social interactions, but I'm inclined to disagree. Part of the trolling art requires social engineering, knowing what to say to either keep oneself out of trouble or to promote mischief in general. I'm not saying all trolls have the eloquence of Maya Angelou, but I would think that it varies more with the actual person than with how they conduct themselves online. And I'm sure most online trolls would control themselves better in the real world, but most trolls would do so not out of fear of punishment but because they understand the difference between the two worlds. I troll online, but I don't troll people offline because I don't want to be treated like an asshole either.
But just like the world online, there are people in the world who don't fear getting yelled at and/or being punched in the mouth for their actions. They'll speak their minds in public (no matter how offensive or who's nearby). They'll do things that bring our blood to a boil (double-parking, talk down to their spouse/child in public, etc). And what do most people do in response? They simply walk away. We accept the fact that there's little to nothing we can do or say to change how these people interact with the world, and I think people should come to accept that, if people like this exist in real life, trolls will be on the internet.
There is a reason that Anonymous advises that one shouldn't "feed the trolls."