[whatshisface]

>If one views the fetus as part of the mother until some stage of conception, it is even simpler to justify.

Many people only believe that one until you use it to justify things other than abortion. For example the mother can get weird permanent cosmetic body modifications done to her (like, I don't know, getting a finger taken off), but the popular support would probably not be in favor of allowing the mother to get them done to her child in the womb. The best way I can explain what the popular opinion seems to be is as non-existence being neutral, as opposed to unnecessarily messed-up existence which is seen as bad.

This doesn't square with utilitarianism where the difference between 0 and 5 is the same as the difference between -5 and 0, but then again it's not like most people's opinions square with utilitarianism.