Lemur:

The Church deals in morality, not popularity.

Abortion has long been held, by the Church, to be little different than murder. Therefore, it considers it sinful to support a politician who unequivocally advocates/supports such a practice in the same fashion as it would decry -- on moral grounds -- a politician who wished to legalize manslaughter or agravated assault. To question the sanity of those following this line of reasoning is unkind -- it is neither poorly thought out nor done frivolously.

Catholics vote in the privacy of a voter's booth like anyone else. How they vote is their business. The Church renders judgement of the morality of one's choices -- including voting -- and encourages any who have 'strayed from the path" to seek Reconciliation.

Because the Church has (rightly) chosen to follow a neutral path on most political issues does NOT mean that the Church wishes to abrogate its responsibilities as a moral force for good.