Thus (with emphasis added):
Consider this from the Catechism of the Catholic Church (no. 2267):
Assuming that the guilty party’s identity and responsibility have been fully determined, the traditional teaching of the Church does not exclude recourse to the death penalty, if this is the only possible way of effectively defending human lives against the unjust aggressor.
If, however, non-lethal means are sufficient to defend and protect people’s safety from the aggressor, authority will limit itself to such means, as these are more in keeping with the concrete conditions of the common good and more in conformity to the dignity of the human person.
Today, in fact, as a consequence of the possibilities which the state has for effectively preventing crime, by rendering one who has committed an offense incapable of doing harm—without definitely taking away from him the possibility of redeeming himself—the cases in which the execution of the offender is an absolute necessity “are very rare, if not practically nonexistent.”
The first two sentences concern morals, but the third sentence is an empirical claim about the state of the world and so is not about morals. The first two sentences are thus, at the very least, doctrina catholica, which Catholics must accept with a religious submission of will and intellect. The third sentence, however, is not; it need only be respected and considered in forming one’s conscience. Catholics need not ultimately agree with it. Compare Justice Antonin Scalia’s conclusion in First Things from 2002.
That is quite true. Thus, it is possible for a Catholic to disagree with the pope and the bishops about when conditions justifying the death penalty are present, without thereby being a bad Catholic. One might still be wrong, but one is not a bad Catholic just for being wrong in that way. Similarly, it is possible to disagree with the pope and the bishops about whether a given war actually satisfies the moral criteria for a just war; but one's being wrong makes one a bad Catholic in that respect only if one rejects one or more of the criteria themselves, as distinct from a particular judgment that one or more of them is, or fails to be, satisfied in the concrete. In both cases, we're dealing with empirical judgments about circumstances; and in making such judgments, reasonable Catholics, like reasonable people generally, can reasonably disagree.
Miller's larger point is this:
Bishops, like everyone else, prefer it when people agree with them, and so some bishops are tempted to enunciate positions and invest them with the authority of their office, even when those positions go beyond matters of faith and morals and depend on particular, even idiosyncratic, views about empirical circumstances. There is a danger, in other words, of bishops leveraging their legitimate authority in faith and morals into the political arena by implicitly passing off empirical judgments as if they were teachings on faith and morals commanding the assent of faithful Catholics.
That is for the most part true, and Miller's post is worth reading just for his argument to that effect. But I am amazed time and again by how widely the distinction Miller invokes above—between moral teachings that bind and empirical judgments that don't—is ignored.
Conservative Catholics are hardly immune from the disease in question, especially on economic matters. I distinctly recall Bill Buckley's reaction, over four decades ago, to John XXIII's Mater et Magistra: "Mater sì, Magistra no." Conservatives often say that the Church should stay out of the boardroom—save, that is, for reiterating the Fifth Commandment—just as liberals often say the Church should stay out of the bedroom—unless of course the bedroom is occupied by a minor and a member of the clergy. But there remains an imbalance. The conservatives' difficulty in forming their consciences according to Church teaching is not as radical as the liberals'.
For example, the conservatives in question generally do not reject the moral principles that have recognizably and consistently belonged to "the social doctrine of the Church," i.e. those moral teachings pertaining most directly to politics. What they do often dispute are particular applications thereof, which depend on empirical judgments about the likely effects of this or that policy. I think they're wrong sometimes, but they're not wrong in such a way as to be certifiably bad Catholics; it's a matter of poor empirical judgment, clouded perhaps by self-interest and cultural prejudice. Liberals, however, go further. They reject moral teachings that have been constantly held and taught from the beginning by the ordinary and universal magisterium: some reject the teaching on abortion; many on sodomy; almost all on contraception. Even the immorality of sexual congress with minors by adults, so apparently clear to all sides today, draws only selective outrage from the Left, whether religious or secular. I have heard no howls from liberals about the recent spate of female teachers raping male students, or indeed about the sexual abuse of minors in the public schools generally; but I do hear a fair amount about the sexual abuse of girls in the home by their fathers or stepfathers, and about the date-rape of high-school girls. It seems that the seriousness of the crime depends both on the gender of the perps and the prior victimhood credentials of the victims. That is classic ideological thinking, which has no place in theology.
At a time when their moral credibility is at an all-time low, the Catholic bishops would do well in political terms to focus on the irreformable principles of faith and morals while leaving to the laity such applications as depend on circumstances. Thus they should continue to make clear that abortion, embryonic stem-cell research, and gay marriage are great and intrinsic evils in which Catholics may not materially cooperate; on other matters, such as the death penalty, war, and care for the poor, they should say only what the Church has always said, leaving the empirical judgments of political policy to those whose business that is.