I don’t know why you’d call that a “fringe belief.” Fully 38% of the public holds that view: https://www.wbur.org/npr/730183531/poll-majority-want-to-kee....

I suspect when most people assert that “life doesn’t begin at conception” they’re not referring to the literal beginning of human life, but the metaphysical question of when “human life that justifies legal protection” begins. That I agree is complex.