I'm not religious, but life beginning at conception remains the only clear answer to the question of "where does life begin". Answers of "brain activity", "independence", and "viability" are not clear and each have their dissatisfactions. The beginning is the beginning, I don't really know how much more clear it can be, and arguments against tend, in my view, to be more about what is personally convenient or politically expedient over being rational, defendable answers.
Now, with that said. I didn't say that life beginning at conception rules out abortion (for one thing, the line of thinking that says abortion = murder presumes that human life is sacred under all circumstances). I could bring up various edge cases such as health and age of the mother, but honestly, it really isn't necessary. When people talk about abortion, it is either from a legal standpoint or a religious standpoint. The religious can debate their ethics among themselves. From a legal standpoint, most legal discussions invariably revolve around criminalization and retributive justice. It is curious to me why we don't look at it from the other direction more often in this case. Instead of focusing on how abortions should be regulated and when they are permissible, why don't we shift the focus to providing the social aid that would make many abortions unnecessary? Universal healthcare, a re-worked foster care system, child support through subsidized daycare and such, contraceptive aid. If you address the economic and social shaming circumstances behind many abortions, I can't help but think that the demand for abortions will steeply decline.
I'd like to think of myself as fairly progressive, but I am not pro-abortion. I think that the need for abortion is predominantly a failure of socioeconomic circumstances, excepting those medical cases wherein the mother is endangered or criminal cases such as rape. By addressing those circumstances, we can lower the demand for abortions without questions of anybody's personal liberty.