Honestly, my guess is that LulzSec is a bunch of crackers that have decided to do something about the public perception of information security. It's kind of a stretch (understatement), but it lines up. They attack indiscriminately, and in every case make fun of any idiotic security practices. When they attack targets that everybody loves to hate, they do as much damage as possible; when they attack targets that everybody loves, they don't release admin passwords or user DBs, they inform the target of their vulnerabilities, and they generally try to be a service to the community. Most importantly, they're trying to make the entire thing /glamorous/. They want people fifty or a hundred years from now to look back on crackers and Anonymous the same way we look back on cowboys, ninjas, and pirates.
They are essentially defacers, though instead of (just) defacing they go for a press release / dox drop. Defacers do it for the attention. You'll often see reasoning on defaced websites such as "We did it for the glory of Iran" or "Maybe you should secure your users data better!" as if to suggest a greater purpose for the actions, but when you string together all of their targets the reasoning almost always falls flat.
Lulzsec may have given some people the wrong impression by hitting Sony and thus suggesting that they were activist minded like the AnonOps program they grew out of, but they'd always been honest about the real reason from day one: "we do it for the lulz". The lulz in this case are inexorably intertwined with the attention seeking.
