Just a few thoughts
Earlier this evening I was browsing 4chan ever in search of the next mindfuck to keep me stimulated.
This is total speculation, but I wouldn't be surprised if many highly frequent contributors to sites like K5 are borderline or full blown ADD cases (Attention Deficit Disorder likely without Hyperactivity otherwise you'd be out bungie jumping).
As evidence, I'd present a couple of observations.
First, scratch a freqent K5 poster, and you'll find an amazing trove of trivia. ADD types are on that end of the human bell curve that is restlessly seeking novelty. In our prehistoric ancestors, the presence of this trait is apparent by the documented fact that H. sapiens bands would often travel a hundred miles to get flint that was just right, whereas Neanderthals would use good enough flint that was close by. The modern equivalent is a passion for absorbing curious facts that don't have much immediately utility -- Google being a major enabler of this behavior.
(I am fully aware of the irony of the above paragraph.)
Second, a characteristic of many people with ADD is that they seek stimulation, and often have poor impulse control. This manifests itself in either conflict seeking behavior, or willingness/eagerness to engage in conflict. ADD types also have the ability to hyperfocus on a task that they find stimulating. A flamewar, or even a heated exchange fits this activity profile perfectly.
Third, ADD people are often humane by nature, but poor at reading others accurately, and are prone to impulsiveness. This leads to negative evaluations of their personalities that often become part of their self-image.
I don't want to be presumptuous, nor do I wish to reduce any person to a diagnosis (which I am not qualified to make in any case), but this piece of LilDebbie's article really stood out for me: "I am a cynical person. Some say I lack that basic human quality known as empathy. Others add that I am a "brutal, cold, calculating reptile." While these claims are not without merit, I was not always this way." This kind of change in self-image often happens when ADD people become teenagers and adults, and the expectation that they are able to read others accurately produces the impression that they don't care about others.
It should be noted that some people with attention deficit problems related to (if I recall correctly) temporal lobe dysfunction really are nasty, although they can't help it. However, your garden variety ADD person isn't really nasty, he's just prone to misreading, saying what comes to mind, and may have a number of coping mechanisms that cause social problems. The tendency not to follow through on things leads to broken promises, which in turn lead to the idea that they are somehow pathologically self-centered.
Finally, don't we all have other things we're supposed to be doing?