Being anti-abortion either causes or has a common cause with believing that life begins at conception. Being pro-abortion causes or has a common cause with believing that life doesn't begin at conception.

It's not obvious a priori that being anti-abortion isn't caused by believing that life begins at conception (but I agree that, except for people deep down the valley of bad rationality, it's way less likely that their morality depends on their definition of the English word life than the other way round).