Tully Borland makes the case in The Federalist.
It is depressing to realize how few people today are able calmly to follow an argument and evaluate it as opposed to heaping abuse upon its producer.
(I have noted the same thing in popular opposition to the work of David Benatar.)
Politics is almost always about choosing between the better and the worse. Both Moore and his opponent, Doug Jones, are flawed character-wise. But character is only one consideration. Equally if not more important are the policies the candidates support. Now Jones is for unrestricted abortion which, as Professor Borland points out, is tantamount to infanticide. Unrestricted abortion is a grave moral evil. So if you refuse to vote for Moore because of his (alleged) sins of 40 years ago, then you indirectly lend support to a pro-abortion candidate. I should think that the gravity of the evil of future abortions far outweighs one man's (alleged) evil sexual excesses of 40 years ago.
According to David French, "There’s no defensible argument for choosing the 'lesser of two evils' in Alabama." But I just gave one!
As Borland points out, if one had a policy of voting only for the morally perfect, one would have to abstain from politics entirely.
UPDATE (12/1). The controversy continues. I won't link to any of it due to its low quality. Much of its rests on the assumption that an argument is good if and only if it leads to a conclusion that the consumer of the argument antecedently accepts. Otherwise it is bad and one is free to mock and malign the producer of the argument.