> Opposition to abortion in the US is entirely premised on Christian ideology and the belief that a human is ensouled by God at the moment of conception

Historically, many Christians (e.g. Augustine, Thomas Aquinas) opposed abortion from the moment of conception, yet didn’t believe in ensoulment until later in pregnancy. This is because they accepted Aristotle’s belief that ensoulment only happened at around 6-12 weeks gestation; but they classified abortion from the moment of conception as a form of contraception, and they believed contraception was a sin. This was arguably the mainstream Christian position from time immemorial up until the 19th century. Maybe a rare position today (especially if you are limiting your consideration to American Christians), but it demonstrates that time-of-ensoulment and morality-of-abortion are (at least partially) logically independent questions

> Science certainly doesn't support outlawing abortion

Whether to outlaw anything isn’t a purely factual question, it is a value judgement. And the question of whose values are correct is fundamentally beyond the scope of the natural sciences. So, science really doesn’t support outlawing or not outlawing anything. It is true that, if we agree on what are the right ethical principles, then science can (sometimes) resolve factual disputes that arise in trying to apply those principles; but if we don’t agree on which set of fundamental ethical principles to adopt, that is a dispute for which science cannot help us