Well, I'm not sure where I was going myself. I guess just that if I compare the number of times I've wanted somebody to get an abortion (0) with the number of times I've wanted to shoot somebody's kid (zillions), it just seems like a good moral justification for the later might be more handy.
So if there's a lively baby-trading network, does it help me to drill a chopstick through little Marky's aorta? I guess your point is that I could purchase Marky, making him mine, and then my job of moral explanation is a little easier, because I only have to worry about offing my own kid... Sadly, I'm not sure Marky has annoyed me enough to justify the expense, and I'm also not certain what justification I have for killing my own kid. Jet skis, children, Tom Hanks -- some things you just want to shoot on sight without having to discuss matters with your accountant.
Your original top post is a great question. I'll check back regarding my answer in about 8 months.
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One thing I've been thinking about as a result of Gregor-Demo exchange above -- here's a plausible assumption about ethics: "Moral obligations must be possible." That is, if I say that a given person is ethically obliged to do or not do something, that person must be able to do the thing.
Given that the capabilities of so many seem so, er, limited, I wonder how many moral obligations would survive that test.