If P2 is true, then why limit the discussion to non-medically related abortion?
Sure, no one wants a mother to die, especially in the case of a non-viable fetus... but if P2 is true, in effect, the medical establishment is selecting who should live and who should die.
No one would stand for this after birth, so why is it ok pre-birth... unless perhaps deep down, short of for a few, P2 isn't as true for the fetus as it is for a living breathing baby outside the womb?
Likewise if P2 is true, why is their not widespread condemnation of IVF?
If P2 is true, why is there not a war on miscarriages?
If P2 is true for some, science clearly shows us that it is not true for all
If P2 is true, and P1 is true... then couples in their 30s and older who are trying to get pregnant are engaging in an immoral act, as they are knowingly killing vast numbers of fertilized eggs in hopes that one will finally implant.
if P2 is true and P1 is true, then birth control, and potentially even practices such as natural family planning are rife with the potential for immoral actions?
If P1 is true, then we've got some major problems with the fertilized eggs which fail to implant... is it immoral for a young couple to try to have children? Their overall intent is obviously moral as part of propagating the species... but knowing that they are also intentionally killing a human being created in the image of God in the process would seemingly call that into question.
If we are talking ethics in this... this is often where an appeal to utilitarianism comes into play, but is that a legit position to consider for those who ascribe to Christian ethics, especially in light of Paul's words in Romans 3?
Granted an appeal to utilitarianism, and limiting P2 aspect only to non-health related abortions can make for a reasoned argument... but when both P1 and P2 fall apart when applied to all abortions / miscarriages / reproductive science / ethics, the narrower case seems pretty vacant, at least to me.
My personal view is that the mother's health needs to be protected, and if that means the fetus has to die in order to save her life and/or her reproductive organs, than that needs to happen. There is almost always another chance at trying again, as long as she lives and hasn't suffered damage to her reproductive organs. As such, I do not ascribe to P2, and if I did, there is no way I could embrace P1 due to the vast numbers of fertilized eggs that never become living breathing human babies. Thus if I can't ascribe to P1 and P2 within the medical domain, I can't ascribe to them in the narrower scope of abortion as a means of birth control.
I'm not trying to convince you that abortion as a means of birth control is moral thing, but that your arguments are not convincing, due to their lacking in universal application and reproductive science. Have you by chance studied Catholic tradition on this? You might find some nuances to help with your arguments, especially from the more contemporary ethics panels. In fairness though, maybe you are ok with the narrow scope, and if that works for you, and I do see its logical flow, I can't fault you for your thinking on this.