Abortion as Infanticide

In response to my post (and Abby Johnson's comments) suggesting that a post-Roe abortion regime could focus more on providers than on the women obtaining abortions, Jonathan Watson suggests that the approach to punishment should borrow from the approach to punishing infanticide:

I do think that abortion is infanticide. I cannot see a reasonable legal argument for assigning a different punishment for ending the life of a human being at X point versus Y point, unless one argues as I have in the last paragraph of this letter.

Some arguments I have seen include:

1) A fetus is less of a person than an infant. Of course, one might argue that this would also entail different punishment for killing an adult than a child than an infant. I don't find this compelling, as it raises the possibility of being able to assign various individuals "personhood" based on arbitrary characteristics (race, nationality, and so forth).

2) The quickening argument, whereby killing the body before movement could be felt by the mother (or some similar argument), thus indicating ensoulment. The image and likeness to God, upon which true personhood ought to be based, is not limited I would say to any point during the developmental process. The quickening line of thinking was also abandoned by the Church once technological advances made determination possible that life was beginning on its own at conception.

3) A fetus has less of an appeal than an infant, as it doesn't physically appear human. I see the same problems inherent here as in the personhood argument in regards to the handicapped, old, and infirm.

Perhaps one could argue that the purpose of criminal punishment of this sort is based not on an object external norm (e.g., all killing is wrong, and therefore, killing a fetus warrants the same punishment as killing an infant, child, adult, etc.) but on internal subjective depravity ( e.g., a person should be more emotionally attached to a born infant), and therefore punished for the greater depravity of the act required to kill an infant than kill an unborn. But, this again makes hash of Catholic arguments in this direction.

On a related note, do you think that one can say that all life is deserving of equal protection of the law, and continue to argue that that life is receiving equal protection when the punishment for destroying that life at different stages is different? It's not something which I have considered before - is it possible that equal protection of two different people under the law might entail different punishment? Would that be the basis of hate crime laws?

I think one could argue that since it is the weakest who need the most protection from external law against physical violence that one could plausibly argue that fetuses and infants, the old, the handicapped, etc., deserve greater protection through deterrance  via imposition of harsh punishments than others in society.