Sarah Palin helped the pro abortion Brown, because she ...
Answer your own questions, Mitt Romney helped Brown because he is not too conservative for his agenda.
Mitt Romney helped the pro abortion Brown, because he did not see him as too conservative for Mitts goals for the GOP, which is to make sure that conservatism is defeated, something that has motivated the Romney family for many decades.
For those of us that accept Brown as the Pro abortion Senator for Massachusetts, it is important to not let him contaminate the national party, especially by making Romney less repulsive to uninformed voters.