all criteria ARE arbitrary. cultures endlessly negotiate and re-negotiate ALL morals, and the majority accedes to them -- and the cultures change thusly. some compromises sit better than others; your desire for an absolute is an abdication of your HUMAN responsibility to evaluate context. we take lives for all sorts of reasons our culture justifies and with which we feel quite okay about collectively: self-defense, war, punishment. your semantic absolutism re human life is just another bid in the negotiations, and one many people aren't buying in the slightest.
if a mother is threatened with death by her unborn child, is it self-defense to terminate the preganancy? what if a mother is *merely* threatened with suffering? i can spin off permutations on these examples all day, while you fisk hoping to find some sense of security in an absolute answer.
much of what you say leads to an appeal to a nameless, perfect authority; or to some unproven inherent quality invested in a definition of "human" that seems very limited. what it means to be human will be endlessly negotiated; and if that seems arbitrary to you, maybe you aren't good at the give-and-take required for participation.
some of us understand that there are no absolutes; that every social decision in life requires context; and that some measure of equitable, moral practice must be found in nuance and compromise. dogma, on the other hand, profanes thought; and the presumption of absolute moral answers strips us all of our earned experience. it's the answer of terrified children who can't look LIFE in the eye, confront the fear of uncertainty, and say "we can only pay attention and do our best."
human existence is negotiation. some plea with hoped-for higher powers; some assert the privilege of an assumed rationality; and others still observe and consider before bidding in humility.
personally, i choose the permissiveness of doubt.
your call, broseph.
