There's something that's just...well, for lack of a better word, special, about being the on the same playing field as everyone else, but working under a completely different set of rules and deciding for yourself how the game is scored.
The best example I can give is how my brother used to grief Counterstrike on TK-enabled servers - he didn't do this by killing his own teammates, or by cheating against the other team. Rather, he would lure his teammates into killing him often enough that they got auto-banned from the server; his rationale was that everyone was too freaking good at CS anyways, might as well make the game more interesting and difficult for himself, at least. :)
When you decide for yourself which game you're actually playing, sometimes the lulz are just too tasty to resist...
That said, DDoSing a bunch of game servers for games that are completely unrelated and haven't done anything in particular worthy of retaliation is moronic. There's no poetry there, just a bunch of children playing around with the 2011 equivalent of AOHell (and yes, I realize that most of them are probably to young to even know WTF I'm talking about).
Think of the Lulzsec activities as more of an art than an act of vandalism. (Most taggers/spray painters feel the same way, and are also known to deface their own stomping grounds)
edit to the downvoters: I'm not defending their actions, just putting myself in their frame of mind
Pseudo-anonymity brings out the worst in people, rather. (Or: If there is no risk of being punched in the face or otherwise given a strong physical disincentive, then behavior tends to deteriorate.)
