Why is Bain Capital hurting free enterprise by donating almost exclusively to Democrats?
There are so many unknowns embedded in your question that I am hard pressed on where to begin.
Maybe it is because Bain is located in the eastern seaboard. Companies there tend to be filled with wishy washy liberals.
It may be due to companies' need to ameliorate draconian or unfair aspects of the tax code. People (both companies and individuals) have the right to petition their government. But I would agree that money of this sort does lead to greater corruption. But on the other hand, the McCain/Feingold Campaign Finance is definitely not the answer.
Maybe it would help if you could document specifically who did what for which particular favors?