Oh, this is a can of worms. I'm not sure but this might be better seen as a discussion of ethics that go all the way in each direction, to eugenics on one side to reciprocal altruism on the other - or zero-sum, non zero-sum perspectives.
I know of Brian Singer from 'animal liberation' and he seems a profoundly moral individual.
It's tricky, because if ?moral? people don't do this kind of thinking, immoral people might (like the Nazi's with Social Darwinism and then pursue it to horrible 'logical' ends) Scientists will often try to look at things without a moral perspective as it distorts the logic. This isn?t because they are immoral themselves, quite the opposite. They attempt to look at a ?fact? i.e. humans kill other humans. They try to view it through an amoral prism to then try to understand why it happens. This might then lead to a situation where you can stop it happening. (Echo?s of social conditioning ? it?s all a balancing act) This is the basis of Hume?s Naturalistic Fallacy. If hypothetical studies are carried out which examine all of the consequences then radical groups supporting eugenics say can then be refuted, as the research has been done. The debate isn't in itself immoral; it would be immoral not to have it.
As we know that sentient animals suffer, we realise it is immoral to kill them. But the argument on infants and the elderly (who have a different level of sentience) is only logically persuasive on the grounds that the sentient people around them wouldn't suffer if they were removed from the equation. It would cause a huge amount of suffering and so isn?t' a viable route. But you only get to this route by asking the horrible questions.
I don't know very much about this by the way, so I might be talking out of my arse. DP does though, I'll ask him about it when he gets in.