The legal concept that a human begins to exist at birth is wrong. The law that defines that is wrong. It is contrary to human nature. That law is invalid and not binding.
Last I heard many of the pro-death advocates had given up on the "life begins at birth" argument. They no longer deny they are ending a human life, but that the life they are ending does not have the protections of "personhood". But their "new" argument is just a cop-out. And it does away with the notion of unalienable rights.