ONE-ISSUE VOTER may have become a dismissive pejorative in our political vocabulary, but some matters are just so central to our worldviews, in one way or another touching every question that society faces, that decisions about them are irreducible. Providence Roman Catholic Bishop Thomas Tobin’s challenge to Rudy Giuliani on abortion — the archetype of these issues — has led various brands of political conservatives to question whether it serves our greater cause to remain defined as pro-life. The conclusion to which they must come is that a contrary definition would likely prove to be a fleeting and destructive illusion.

The battle over embryonic-stem-cell research — which, itself, is a stand-in for the entire first wave of brave-new-world moral questions — required that abortion defined life down. The proclaimed right to a fail-safe, life-destructive contraception has allowed us to pass ever-compounding boundaries beyond prudence and good taste. The depersonalization of those lives that conception creates — and the families that they should imply — has softened the definition of marriage. These are not ultimately distinct issues on either side of the ideological line that separates those who see in them freedom and those who see the machinations of evil.

Practical considerations are, of course, allowed. It is a deranged purity that insists that short-term compromises (which are not, of themselves, wrong) cannot be made in advancing a cause. A pro-abortion senator who puts the government in the hands of a pro-life party can serve to inch our nation toward a proper stand. State-level officials have less effect altogether (for the time being).

But a pro-choice Republican president, which, let’s be honest, includes any candidate who takes the personally opposed-publicly removed pass, would be too decisive. A line would have been crossed. It would mean, essentially, that we were ruled by two “parties of death,” one full throated, the other still mumbling under its breath.

The obvious objection to taking abortion as an absolute guide for a presidential race is that other matters can override, in their urgent prioritization, long-term questions of national identity. If the very existence of the nation is threatened, and only one candidate can be trusted to protect it, then the cultural battles must be put on hold.

I, for one, am not convinced that we face such circumstances in the next election cycle. Oh, the very existence of our nation is threatened, all right, but it is increasingly clear that the American public is not going to allow any president to fight the war for our survival the way in which it needs to be fought until there’s another horrific wake-up call, probably making 9/11 look mild in comparison. At such time, hawks will find their way open to power regardless of their positions on social issues. It would therefore be folly, from a cultural conservative’s point of view, to concede that ground in anticipation of urgency.

As for fiscal matters, there’s a real danger that a society whose moral compass points toward a nihilistic pole would discover that conservative economic prescriptions — prescriptions that I generally support — merely enable an avaricious business class and a government with insufficient concern about its own citizens. To stray from principles that flow from the sanctity of human life is to plunge into labyrinthine brambles, ever thicker with thorny questions answered in deference to our addiction to profit and material wonders.

In the worldview of modern conservatism, a basic insistence on morality, founded most fundamentally in the right to life, is what permits freedom. The principles that this worldview suggests are meant to structure society such that its various interests can remain in healthy balance without government interference, enabling government — with its powers of compulsion and susceptibility to corruption — to remain limited in its scope. Moral behavior ought to be enforced through the pressures of responsibility, and the alternative to an insistence on self-reliance and personal restraint is an allowance of public dictation, of regulation of our every decision.

In a society with nigh upon unlimited rights to abortion, the single greatest and most universal responsibility, parenthood, may be rejected with the need to develop neither a mature approach to the behavior that initiates it nor restraint of a primal urge. The untrammeled availability of this filicidal biological “undo” creates a mindset that begets conclusion after conclusion that nothing has consequences of such magnitude that rationalizations and modern science cannot dispel them.

For these reasons, I just don’t think that I would be able to reason my way around to voting for a presidential candidate who is not pro-life.

Any conservatives, or Catholics, who believe that they could do so ought to re-examine what it is that they ultimately support, and what it is that they actually believe. As for those who are neither, the place to start is with that line between freedom and evil and the talking-point foci through which it runs.

Justin Katz is administrator of anchorrising.com, a public-policy-discussion Web site.