An important first principle to remember:
When I was younger I used to read a lot of Tom Clancy. If a tightly wound plot, espionage, and gadgetry are your thing, he's fun. But he's a bit less pleasing to read now. Clancy does not shy away from a good guy/bad guy kind of characterization--it's clear who they are. The good guys, however, find themselves in a dangerous world where many diplomats, agents, provaceteurs, soldiers, terrorists, etc. pursue malicious goals with no moral compunction.
Clancy's heroes, on the other hand, are notable for their boy-scout warrior code, their sense of fair-play, honor, concern for noble values and traditional institutions like the family. There are many minor characters of course who fill in the pages who exhibit more of a muddled sense of right and wrong, but the major characters nonetheless are on either side of the moral hemisphere.
Except for one thing: in every Clancy novel the good characters are faced with situations, problems, where they have to compromise and do something seemingly immoral for the sake of a greater good. Most of Clancy's works can be read as a sort of apologetic for this kind of statecraft, and particularly for the importance and need of state agencies (like the CIA) that are willing and able to bend a few rules so lives can be saved: a realpolitik. The moral of his stories: sometimes you just have to get your hands dirty, and we should be grateful that some are willing to do this; we live in peace and security because of their willingness.
Many people I talk to, people who would purport to have an objective sense of right and wrong, happen to share the same sense of morality as the Clancy good guys when push comes to shove, which fundamentally is the utilitarian one: the right thing to do is a consequence of a calculation where we figure out how to achieve the best for the greatest amount of people. Accordingly, in such a moral calculus, no action is strictly "off-limits". In certain grave situations, even heinous acts may need to take place to save lives. It's what I call, the Tom Clancy (or perhaps, the Jack Ryan) morality--which is really not all that different (except for the details of their personal lives) with the James Bond morality.
The Catholic understanding of morality is different.
What most don't seem to get is, the Church holds that evil can never be done for the sake of a good end. Full stop.
Furthermore, some actions, like the taking of innocent life, are always evil, and so we can never rightly intend such actions. This is why, for example, the Church has always opposed the reasoning that led to the atomic bombing of Hiroshima and Nagasaki. These actions are usually defended with a nuanced moral calculus, that amounts to the criterion of saving more American and Japanese lives in the long run. No matter. The intended (and as G.E.M. Anscombe pointed out, what you knowingly do you willingly intend) targeting of non-combatents in war is always evil, as is any taking of innocent life. It simply can never be justified. The torture of even one innocent babe to save the lives of the whole world, and other moral scenarios, illustrate this.
So in discussions of war, statecraft, realpolitik, particularly apposite the whole Middle East-Iraq-Israel situation, many find themselves apoplectic when confronted with things the Vatican says in response. Why? Well, my guess is they have implicitly adopted a kind of consequentialist thinking that says, sometimes things are so bad that you've got to do bad to clean it up.
But the Church says, the stakes are never so bad that evil becomes justified. And it wants to be heard loud and clear. And it knows and wants others to know well the many evil consequences that always come from war.
A deep consideration of this principle is critical for understanding the Church's invective against war: the principle that evil can never be done, that is the reason why the Church can say war is "a failure," "always a defeat for humanity," "the failure of all true humanism," "an adventure without return," etc. War as it is now considered by the Magisterium can only be legitimate if it is a defensive action. (See CSD, 496, 497)
The Church teaches that "violence is never a proper response." This strikes many as limp-wristed, if not naive and simply stupid. What about self-defense? they say. Well, even St. Thomas noted that a private individual can never intend to take another life; only the state in certain circumstances can even do that. Even in defense, a private individual cannot intend to kill; he can only intend to defend with force. I won't get into the differences here; if they are not obvious, well, that's a whole other discussion (cf. the end of this post).
Violence as aggression however is what the Church is condemning; and this is always evil. Beginning a war, or covert ops, or whatever, for some good end, can never be justified. This does put most statecraft outside the pale of Catholic morality. Yes, it's true--part of the inherent problem of the modern state.
The Church is clear: "One may not do evil so that good may result from it."(CCC 1761) For individuals or states. The use of force (as distinguished from violence) can only be used by the state as a defensive measure, and then only according to strict rules (e.g. The reasons for just war).
I am very much pro-Israel, and quite sympathetic to its concerns. However, if Israel decides to wage war which permissively results in the deaths of non-combatants, this cannot be justified. The reasons for war may be justified, but certainly the kind of warcraft (in war) that relies on permitting collateral damage is evil and unjust. If it is decided that proportionality can be ignored, this too is an evil.
Admittedly, the situation is more complex with terrorism and urban warfare. However the tactics are conceived, it is still true, that evil may never be intentionally done, for any reason.
[If someone wants to argue for double effect, this is typically a red-herring, or perhaps just simply a misunderstanding of double effect. For St. Thomas, double effect can only apply to unintended consequences. (Cf. G.E.M. Anscombe's point, very important, that what we knowingly do we always intend. Also cf. St. Thomas on the difference between ignorance and involuntariness.)
Here is St. Thomas's brief discussion of the issue, in ST II-II 64.7. I find most people are surprised by his conclusions:
I answer that, Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental as explained above (43, 3; I-II, 12, 1). Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists, "it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense." Nor is it necessary for salvation that a man omit the act of moderate self-defense in order to avoid killing the other man, since one is bound to take more care of one's own life than of another's. But as it is unlawful to take a man's life, except for the public authority acting for the common good, it is not lawful for a man to intend killing a man in self-defense, except for such as have public authority, who while intending to kill a man in self-defense, refer this to the public good, as in the case of a soldier fighting against the foe, and in the minister of the judge struggling with robbers, although even these sin if they be moved by private animosity.Consequences may be anticipated or guessed at, but an act can only ever be justified if it is good or at least morally neutral. If some evil may result in an action, as an unintended consequence, a side effect, the good that is intended must be a result of the act itself and not the peripheral evil. The evil cannot be intentionally willed; only guessed at and tolerated, proportionally.
Double effect only applies to good actions, never evil ones.
And if the guess amounts to, more evil may result from this act (i.e. proportionality), or even, some evil will certainly result from this action, then it cannot be done (since evil can never, ever, willfully be done). In any situation, the moral actor must always try to avoid all evil that is in his power, perhaps even by abstaining to act if proportionality demands. Since we have minds that can anticipate future consequences, we can be held responsible for evil that we did, or should of, anticipated as probable. (e.g. why a drunk driver who has lost the capacity to reason well is still held responsible for what he does, based on the fact that he should have known better; or why someone in a fight who hits someone so hard that they accidentally kill them is guilty of murder and not simply manslaughter--the response, I didn't mean to, as any parent knows, is usually fallacious) A fallacy in consequentialism is the denial of any distinction between forseen and intended consequences. Here is an excerpt of a reviewer summarizing Anscombe's point:
Here is a great article on Anscombe if anyone wants to know more about her; one of the greatest Catholic philosophers ever.]
In Modern Moral Philosophy Anscombe singled out Henry Sidgwick for taking a step in thought with fatal consequences. He held any foreseen consequence of a voluntary act to be intended. She distinguishes a foreseen effect of an action from the intention with which it was done. The intention does not lie only in the end for which it was done; it comprises the chosen means as well, and the act is bad if those means were bad. But the action may have an unintended but foreseen side-effect. The end was not attained through the side-effect; if it had been, that subsidiary effect would have been the means, or part of the means, to that end.
Anscombe accepts the principle of double effect, which she prefers to call that of “side-effects”, but thinks that of itself it does not say when an act with a bad foreseen but unintended side-effect is permissible; it merely allows that it may be permissible. Further principles are required to determine when the side-effect renders the action bad. Obviously it does so when an alternative course of action was to hand, or when the end is trivial;
Anscombe suggests that it may also do so when the side-effect is both immediate and certain.
She complains of the abuse of double effect by some Catholic moralists, who think bad actions can be excused by “directing the intention”. This means selecting one of several descriptions under which the act is intentional, and nominating that as one’s intention, so that all else becomes a side-effect.