During their deliberations, the Bishops had received a private letter from then-Cardinal Ratzinger that was later made public. In it, he said:
It is the teaching of the Catholic Church from the very beginning, founded on her understanding of her Lord’s own witness to the sacredness of human life, that the killing of an unborn child is always intrinsically evil and can never be justified... To make such intrinsically evil actions legal is itself wrong. This is the point most recently highlighted in official Catholic teaching. The legal system as such can be said to cooperate in evil when it fails to protect the lives of those who have no protection except the law. In the United States of America, abortion on demand has been made a constitutional right by a decision of the Supreme Court. Failing to protect the lives of innocent and defenseless members of the human race is to sin against justice. Those who formulate law therefore have an obligation in conscience to work toward correcting morally defective laws, lest they be guilty of cooperating in evil and in sinning against the common good. (emphasis added)
That is standard Church teaching about the question of cooperation with evil. And so, many people point to this notion of "proportionate reasons" when approaching the voting decision. But in fact, our Bishops have gone further, and have significantly raised the bar for making a decision whether to vote for a "pro-choice" candidate because of their other positions. In their document Forming Consciences for Faithful Citizenship, the Bishops have said:
When a Catholic does not share a candidate’s stand in favour of abortion and/or euthanasia, but votes for that candidate for other reasons, it is considered remote material cooperation, which can be permitted in the presence of proportionate reasons.
Specifically with respect to abortion, the Bishops responded to errors that are made in applying Church teaching that can disort our defense of human life. They said:
There may be times when a Catholic who rejects a candidate's unacceptable position even on policies promoting an intrinsically evil act may reasonably decide to vote for that candidate for other morally grave reasons. Voting in this way would be permissible only for truly grave moral reasons, not to advance narrow interests or partisan preferences or to ignore a fundamental moral evil. (35, emphasis added).
The Bishops don't point this out, but in making our voting decision it is vitally important that we don't consider it in isolation. Instead, we have to look at the reasonably foreseeable consequences -- in other words, what will happen if this flawed candidate is elected? In the case of the Presidential election, there are substantial foreseeable consequences: as many as two possible Supreme Court nominations, dozens of Circuit Court and District Court nominations, and appointment power to many key policy-making positions in the Administration where regulations are developed (just think of the HHS Mandate and you'll know why this matters so much). Will the candidate's future actions work to ameliorate the situation, leave it intact, or make it even worse? One also has to take into account the likelihood of a candidates' positions becoming reality -- they may be nice campaign promises that are in keeping with the positions of the Church, but if they may have no chance of being passed, then what good are they?
The first [temptation] is a moral equivalence that makes no ethical distinctions between different kinds of issues involving human life and dignity. The direct and intentional destruction of innocent human life from the moment of conception until natural death is always wrong and is not just one issue among many. It must always be opposed. (28, emphasis added)