If you're referring to the reference to the law on accidental harm to pregnant mothers in Exodus it's irrelevant to the question of when life begins. I can think of many reasons why courts would be lenient about sentencing regarding harm of unborn compared to born human beings. For example, if you when driving accidentally bump a man on the road and he dies but he was a hemophiliac, is it not just for a court to take that into account when sentencing? You did kill the man, but extenuating circumstances give the chance of leniency, justly deserved.