I've blogged about these issues many times now. Readers are probably bored to tears! But these issues are incredibly complex, and I'm not even sure I understand them correctly. But here is my attempt to outline the relative position of Church teaching on these three key topics. The starting point must be Cardinal Ratzinger's oft-quoted comment: "There may be a legitimate diversity of opinion even among Catholics about waging war and applying the death penalty [but not about abortion and euthanasia]." We all know what many right-wing Catholics conclude from this! But let's actually delve deeper. This means getting into the different levels of the Church's teaching authority ("magisterium")
As I understand it, there are three basic levels of teaching.
First, infallibly defined doctrine. If you dissent from this, you cannot consider yourself Catholic, and you have embraced heresy. But before you accuse me of cheerleading for a return of the Inquisition, let's be quite clear: as Stephen Bainbridge points out, there are relatively few formally-defined infallible teachings. These mostly concern themselves with teachings pronounced by ecumenical councils (there have been 21) and by the pope acting ex cathedra (there have been 2). These doctrines comprise the deposit of faith, and as noted by Vatican II's Lumen Gentium, "must be adhered to with the obedience of faith". There is also the concept of infallibility according to the ordinary magisterium, or (in the words of Archbishop Bertone), a concept "expressed in the fact that all the Bishops (including the Bishop of Rome, who is the Head of the College) give a common witness." This requires no formal declaration, and was also set out in Lumen Gentium. What component of the ordinary magisterium is infallible or not is a subject of great controversy among theologians, and it is not something I wish to discuss (the border is, to say the least, fluid!).
Second, the category of non-infallible Church teaching in the domain of faith and morals that is nonetheless part of the ordinary magisterium. Although not infallibly defined, it does require "religious assent". Again, this is made clear in Lumen Gentium. If one dissents from these teachings, one is still Catholic. But one cannot do so, absent very good reasons.
Third, prudential judgments defined as the "application of Catholic doctrine to changing concrete circumstances" (Cardinal Dulles's language). As this is by its nature in the realm of uncertainty, one is not necessarily bound to adhere to Church statements in this area.
Now, what of my three examples: abortion, war, and the death penalty? First, I think it is fair to say that the teaching that the taking of an innocent human life is always and everywhere wrong is an infallible doctrine. That would hold for both directly-procured abortion, and in war when non-combatants are deliberately targeted (think Dresden, Tokyo, Hiroshima, and Nagasaki). These actions are evil in their object, and there is no need to address intent or circumstances. So far, so straightforward.
But the Church does not teach that war and the death penalty are always and everywhere wrong, or wrong in their object. Their moral licitness depends on other factors, notably intent and circumstance. We must move to the next step. Here, it is important to note that Church teachings at this step should not be understood as prudential judgments, but as part of the second category above, namely, non-infallible teaching according to the ordinary magisterium. As Zippy says, they refer to as principles governing circumstances rather than judgements about particular circumstantial facts. They are not prudential judgments. Church teaching in these does indeed attempt to carve out situations under which war and the death penalty may and may not be immoral. For war, the strict just war conditions must be followed. For the death penalty, there needs to be no bloodless way of defending society for it to be licit. These are teachings about morals, requiring "religious assent".
But many who disagree with recent Church statements on war and the death penalty claim not to disagree with the principles, only to their application to particular circumstances. For example: Do the just war principles hold in this conflict? Was the execution of this person immoral? But note something incredibly important. Many of the Church's statements on abortion are also firmly of a prudential nature. The only infallible statement is that the taking of an innocent human life is wrong. It follows that there can be no "right" to take life. So if the Church says penal sanctions must be applied by the state for abortions, it is applying infallible teaching to the concrete circumstances of abortion in modern society, and implicitly assuming that this will succeed in protecting the unborn. To deny that penal sanctions ever work might be a peculiar opinion, but it is a valid one. Many countries where abortion is illegal still have non-negligible abortion rates. And even accepting criminalization, should doctors, women, or both be punished, and why? Again, prudential judgment! Another argument is that the pro-life movement must focus all its efforts on overturning Roe v. Wade. But an equally valid prudential judgement is that while the principle underlying this case (that abortion is a right) is immoral, its overturning will have minuscule effect, as most states will retain legal abortion. And, of course, it is possible to argue that what actually works best in reducing abortion is putting into place supporting economic and social policies that facilitate the rearing of children.
So, how can we sum up?
First, some of the teachings pertaining to war and the death penalty are clearly teachings about morals under the ordinary magisterium, in particular, the underlying principles. Many who reject Church teachings on these issues, while they refer to individual circumstances, are actually implicitly rejecting principles. For example, how many of these Catholics accept the principle that the war or the death penalty should not be an instrument of vengeance? It is in this sense that Justice Scalia dissents from Catholic teaching, by refusing to adhere to the moral principles pertaining to the application of the death penalty. And when it comes to war, how many truly take concepts like "last resort" and "evils and disorders graver than the evil to be eliminated" seriously?
Second, as noted above, while a directly-procured abortion is always intrinsically evil, dealing with it in modern society calls for prudential judgment. If you can so readily dismiss the Church's prudential judgment on issues like war and the death penalty, why are you supposed to automatically hold the prudential judgments pertaining to abortion to a higher standard? And there is another point. The idea is to try to figure out, using reasoning, whether something is right or wrong. "Prudential judgment" is not (as many claim) a license to ignore. For, as noted earlier, not all prudential judgments are equally valid. The Vatican was quite right about the Iraq war, and about the execution of Saddam Hussein. One could also contend that saying that having no laws against abortion would not affect abortion is a little bizarre. But the hypothesis that repealing Roe v. Wade will lead to fewer abortions is untested. We honestly do not know.