I think Roberts' motivation is pretty basic -- fear and pride. He saw this as an opportunity to attach his name to something "historic", and he wanted to receive praise instead of criticism from the academy and media which are both overwhelmingly liberal.
To overturn the law, not only does Romney have to win, but Republicans have to keep the house and turn the senate. THEN, the squishy Republicans have to demonstarate some spine, vote in solidarity and use some tricks like reconciliation, all the while being savaged by the media. THEN all the liberal lawsuits that would inevitably follow would have to be overcome.
Folks, it isn't going to happen. Even if the law is overturned, the damage to the constitution from this decision remains.
How lost we would be if not for the fact that the Lord is in control.