I wonder if Vick didn't really have an interest in the dogfighting itself, but saw it as a way to stay connected with his old friends from home.
Think about it this way: you know a guy from your neighborhood who's a supermillionaire, and he considers you and your neighborhood to be a part of his "roots." You want to start a big dogfighting business, but you don't have the capital to get it started. Why not call Mike and see if you can get him to invest in it? You'd get the money you need to run your gambling ring, and he'd get to claim "street cred" by being involved in it.
From Vick's perspective, once he'd been peer-pressured into putting up the money to get the dogfighting ring established (buying the property, etc.), he'd naturally have an interest in its success: he'd want some kind of payoff for the money he spent on it. That interest would naturally lead him to increasing involvement in the organization.
This explanation doesn't excuse the fact that he was directly involved in an illegal gambling establishment that ritually tortured and executed dogs for sport. On the other hand, I can't imagine any other way to explain Vick's involvement without writing him off as a sadist. The world will probably never know what his real motivations were, because history has shown us that the most efficient way for a pro athlete to ruin his career is to open up to the press. Vick's best move, now that he's been caught redhanded, is to keep as low a profile as he can until he completes his sentence, and then live as quiet a life as he can while he considers a comeback. He didn't have the wisdom to get rid of his thug friends, and he didn't have the conscience not to torture dogs, but he might have the sense to keep mum about as much as he can for as long as he can.
From an Atlantan's perspective, I'm glad that we now have a starting quarterback who passes better than he rushes. I suspect the Falcons' receivers share that sentiment.