The Pittsburgh Steelers have signed convicted animal abuser Michael Vick to a one year contract as backup to Ben Roethlisberger. There are a wide variety of reactions to this from "OH MY GOD I'M GOING TO GO ROOT FOR THE PATRIOTS NOW!" to "Whatever" to "Who?" to "Where are we going and what's with this handbasket?"
The short form answer is simple:
If it makes money for the Steelers organization, they're going to do it. Moral outrage doesn't mean a damn thing to them, unless it's backed up with a large scale boycott of Steelers product (jerseys, tickets, concessions, etcetera). Pittsburgh being what it is, at most there may be a small (<.05%) drop in revenue as a result of this. Season tickets will still require you to be the heir to someone who had them, and all the other income sources won't dry up, either.
This also goes to the idolization of sports heroes as role models for off the field behavior. In all cases I've seen, just because you're good at sportsball of any sort doesn't mean you're a great person in non-sportsball scenarios. Let's not mix on-field and off-field actions.