Abortion is morally wrong

[JuliaL]

Moving from that assumption, why have we decided that killing is morally wrong?

Societies are subject to descent with modification in the same way that organisms we generally view as such do. Essentially, societies in which everyone goes around killing on a whim are not as likely to succeed as those which develop a taboo against the practice. They are replaced by the less violent ones. Those are the ones we observe.

I wish to differentiate between 'objective' morality meaning a uniform morality as observed by participants and 'absolute' morality meaning a uniform morality as observed by any observer. I believe in the first. I don't believe the second exists. Often in discussion, I find that theists mean 'absolute morality' when they say 'objective morality.' Objective morality is subject to descent with modification and evolves differently in different environs.

Bacon: good for breakfast, bad for the pig. I'm not willing to grant that the pig's viewpoint on bacon is of the same weight as my own. I expect a pig society would develop the opposite inclination. This is much as we see claims for authority from theists of any particular sect.