My own personal opinion on why the bishops were not more definitive on voting decisions has to do with the complexity of candidates’ positions on a whole variety of social and moral issues, including those same candidates’ often wavering, changing, or tentative views on abortion specifically. Then one has to consider the value of one’s vote in the larger calculus – and I don’t mean in the earlier stages of electioneering, but when it comes down to final decisions between/among a limited field of candidates, who remain viable after others have been eliminated.
Candidate A favors constitutional amendment banning all abortion, permanently, throughout the U.S., regardless of circumstance. Also favors massive military build-up, privatization of all social services and agencies, flat tax regardless of circumstances, no path to citizenship (or other assimilation) for illegal residents, and prayer in public schools.
Viable support among the electorate is 2%. Candidate A, with such narrow public support, is eliminated as a serious contender in the general election, stabilizing at 2%.
Candidate B favors support for Roe v. Wade, distribution of contraceptives in public middle schools, institutionalizing of gay “marriage,” no parental consent relative to teenage abortion, open borders with Mexico and Canada, expanded funding for embryonic stem cell research, and federal protections for physician-assisted euthanasia. Candidate B unfortunately enjoys wide support among the general public, ranging from 45% to 60%.
Candidate C favors limitations on Roe v. Wade, but not prohibition of abortion altogether. Opposes DOMA, supports DADT, but does not support federal intervention or pressure on the several states regarding their own marriage regulations. Does not commit to federal funds for embryonic stem cell research, but in the past has been quite supportive of it, and of contraception availability in public schools. Is neck-and-neck with Candidate B.
Candidate D has a similar position to Candidate C on abortion, going further than that with parental consent laws regarding not only abortion but also contraception. Other positions are similarly more in line with Catholic moral positions than Candidate C. However, Candidate D is unlikely, even with every Catholic voting for him, to win more than 15% of the general electorate, and every theoretical contest pitting him against the above candidates, show him taking votes from Candidate C, nearly ensuring a victory for Candidate B.
…and there are a whole host of permutations and combinations when it comes to issues and electability. That’s why, i.m.o., the bishops worded it that way. There are several issues that are “black-and-white.” However, the reality of final contests, the electoral college, etc., make it important for Catholic voters to use their votes wisely.