John McCain hasn’t been very popular in some quarters. It seems that his party doesn’t like him nearly as much as Barack Obama and even Hillary Clinton are liked by their party. Conservative talk-show hosts have even complained loudly that they would vote for his opponent rather than him because it would be bad for conservatism to have him at the head of the GOP and running the country.

When facing a choice like this, it is refreshing to be Catholic. What’s good for conservatism or bad for conservatism doesn’t matter to us — “convervatism” is against Church teaching as often as it’s for it. As Catholics, we only care about the common good — and the pre-eminent issue affecting the common good is abortion.

It’s important to note why it’s the preeminent issue. Here are three reasons.

First, in justice abortion must be opposed. As the bishops recently put it, “There are some things we must never do, as individuals or as a society. … These are called ‘intrinsically evil’ actions. They must always be rejected and opposed and must never be supported or condoned.”

Second, human rights are fundamental. If we don’t have human rights, it doesn’t matter whether we are prosperous or not, have health care or not, or who we are at war with. In the bishops’ words, the right to life is “the most fundamental human good and the condition for all others.” A society that denies the right to life will soon be willing to deny other human rights.

Third, abortion corrodes our system of laws. In order to justify an out-of-whack right like the “right” to abortion, we have out-of-whack jurisprudence. As the bishops put it, “A legal system that violates the basic right to life on the grounds of choice is fundamentally flawed.”

Now, McCain doesn’t have a perfect pro-life voting record. The significance of that shouldn’t be diminished: He has said he is for federally funded embryonic stem-cell research. To be clear what that means: He wants to force us to pay lab scientists for research experiments in which they kill human beings.

All the same, a vote for McCain would be better than a vote for either Barack Obama or Hillary Clinton.

Shortly before he became Pope Benedict, in his letter to Washington Cardinal Theodore McCarrick, Cardinal Joseph Ratzinger explained what a voter’s attitude should be toward abortion.

“There may be a legitimate diversity of opinion even among Catholics about waging war and applying the death penalty,” he said, “but not, however, with regard to abortion and euthanasia.”

But he added that a Catholic must sometimes vote for a candidate who is not perfect: “When a Catholic does not share a candidate’s stand in favor 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.”

In other words, abortion is the preeminent issue. A Catholic’s obligation is to cast the vote that will best advance the culture of life. When advancing the culture of life isn’t possible, our obligation is to case the vote that would best protect the culture of life. And if that’s not possible, our obligation is to cast the vote that will do the least harm to the culture of life.

Both Obama and Clinton have records that are, for all practical purposes, 100% pro-abortion. Obama wouldn’t even protect children born alive by mistake during abortion attempts. If either of them wins, as one pro-life blogger pointed out, we will get:

• two more Supreme Court justices who consider abortion a right, plus more than a hundred Federal court appointments to foul our justice system for another 50 years,

• federally funded embryonic stem-cell research,

• federally funded cloning and “chimera” research,

• federally funded abortion on demand,

• abortion in military hospitals,

• federally funded abortion overseas,

• vicious regulatory attacks on pro-life doctors, nurses, clinics and non-profit groups,

• the repeal of conscience-clause exceptions for doctors and pharmacists,

• efforts to reclassify churches and pro-life activities, threating their tax-exempt status,

• “the Freedom of Choice Act” (FOCA), which is like the Human Life Bill in reverse — a federal statute mandating abortion on demand in every state,

• the end of abstinence education, and

• the end of the highly successful approach to AIDS in Africa that stresses abstinence and monogamy.

That’s to say nothing of nationalized health care, which in other countries has become a synonym for rationed care and has brought inexorable pressures against respect for the dignity of human life. Under national health care, bureaucrats will determine that limited resources go where they can do “the most good.” So the system will simply refuse to cover high-risk pregnancies or humane end-of-life care for the elderly and the dying.

That’s also to say nothing of the appointments presidents make to federal agencies. The Obama and Clinton teams will appoint political operatives to agencies across the federal government. Many of them will be pro-abortion activists. They will build their ideology directly or indirectly into countless regulations, national policies and guidelines — and not just in our schools, and federal welfare programs, but in the myriad programs the government is involved in.

All of this is not a done deal yet. Far from it. We started by saying that McCain isn’t as well-liked in his party as the leading Democrats are in theirs. But important research showed that, in the last election, many Democrats who didn’t particularly like President Bush voted for him anyway —because of his pro-life stand.

Sometimes it isn’t the “most liked” candidate who wins, but the one whose more principled stand means we’ll vote for them whether we like them or not.