At the heart of the abortion debate is a religious belief — that life begins at conception. This is not a scientific belief; this is a religious dogma that often religious people try to dress up as scientific. But, it’s not.
Naturally, science hasn’t been able to come up with a super solid answer as to when life begins, which is part of why the “life begins at conception” thing has taken off. The religious right has one simple easy to understand answer, and science says “it’s complicated.”
People gravitate toward the simple answer, because it helps them feel safe.