hence, we make laws to embody popular social contracts. it doesn't mean those "rights" exist beyond a society in its given time, place, and context. your belief that folks have a right to live is a product of your participation and indoctrination in the society you live in. if you were born in borneo in the 1500s, you'd be killing babies and women and the infirm along with the best of 'em, and you wouldn't feel even a whit of guilt, because, to you, it'd be the right thing to do.
cultural relativism sucks, but wotcha gonna do?