The question of "when does life begin?" is deceptive. Life does not begin at conception with each life. Life began some 3.5 billion years ago and has never stopped. Each life continues unbroken from other lives. If the complaint is that any point we choose is arbitrary, well this is what nature gave us. The only logical point to begin from is when the new life separates from the old.

And frankly, nature eats way more babies than adults.