The answer to this necessarily involves moral philosophy, which few of us ever think about. St. Paul touches on it in Romans 3:8, when he condemns doing evil so that good will come about, and Biblical morality is the foundation of Catholic moral philosophy. Part IV of the post on McBride addressed the question in greater length, but the basic idea is this:
- Catholic moral philosophy: you may never intentionally do evil so that good may come about. You may do an action for a morally good purpose which has negative consequences, so long as you don't intend the negative consequences. The example I used was the Death Star: it's moral to blow up the Death Star (since it's generally not immoral to kill your enemies in battle), even though innocent people were certainly on it. But to intentionally target the innocents would be immoral.
- Utilitarianism: The ends justify the means, and the moral question isn't on the act itself (as in Catholicism) but upon the results of the act. Whatever produces the greatest benefit for the greatest number of people is the best approach. So an evil thing can be done if it produces a good benefit, while a good thing cannot be done if it produces an evil benefit (although instead of evil and good, they'd prefer terms about less or more utility/pleasure).
Most Americans in recent years tend heavily towards utilitarianism, which is disturbing, since it's a heavily atheistic, amoral philosophy which has been responsible for millions of deaths in the twentieth century alone. It's this knee-jerk utilitarianism which explains their confusion on the life-saving abortion issue, and the utter inability of most commentators to even grasp that there's another side to the argument (namely, that murder is never okay, regardless of the ends being pursued).
That said, some of the ideas behind utilitarianism would still revolt the average American. For example, most people are fine with bombing enemy territory, even though we know that innocent people will be killed -- the Iraq war's broad support made this much clear. But most people are still (I hope) against intentionally executing innocent people. For example, if we knew it would end the war in Iraq to round up and execute 1000 children, very few people would support it (and those who would, we'd condemn as monsters). This is true even if we knew that continuing the war effort would allow more than 1000 kids to be inadvertantly killed. At some basic level, we seem to have a collective conscience which can distinguish between intentional evil and collateral harm. Staunch utilitarians like Peter Singer lack that conscience. He's argued, for example, that we should let handicapped infants die, because it's for the "greater good."My concern, after writing my original post, was that it made Catholicism seem incredibly restrictive. If Catholic moral teachings were followed, we never would have firebombed Dresden or Tokyo or nuked Hiroshima or Nagasaki, potentially allowing the Second World War to claim countless more American lives, and we would let pregnant mothers die, out of a refusal to provide life-saving abortions. But Peter Singer's managed to show how incredibly restrictive utilitarianism is in a recent post to New York Times' philosophy blog, entitled "Should This Be the Last Generation?". Singer ultimately answers his question in the negative, but another utilitarian he cites to, the South African philosopher David Benatar, wishes our children would never be conceived:
One of Benatar’s arguments trades on something like the asymmetry noted earlier. To bring into existence someone who will suffer is, Benatar argues, to harm that person, but to bring into existence someone who will have a good life is not to benefit him or her. Few of us would think it right to inflict severe suffering on an innocent child, even if that were the only way in which we could bring many other children into the world. Yet everyone will suffer to some extent, and if our species continues to reproduce, we can be sure that some future children will suffer severely. Hence continued reproduction will harm some children severely, and benefit none.
In my earlier post, I'd noted that while (given the examples I was using), Catholic moral philosophy seemed the more restrictive of the two, that utilitarianism demonized all sorts of innocent activities. I mentioned driving a car. Singer mentions eating meat (because of its impact on climate change, not on the cow, incidentally). And Benatar is against having kids. Utilitarianism is, in many ways, a sick philosophy. It justifies nuking unarmed civilians to shorten a war, but not having kids or cheeseburgers. And hopefully, the candor of Singer, &c., makes it clear that it's not the morally libertine option it may parade as. It's far more pharisaical and rule-bound than even the parodies of Catholicism.