So explain why the Founding Fathers didn’t outlaw abortion.
They did. In the Fifth Amendment. And, the Preamble explains what it means. You know, "secure the Blessings of Liberty to ourselves and our Posterity," and all that.
I'm sure if they thought Americans could become so corrupted that they would accept the "legality" of butchering babies, they'd have been more explicit for you. Not that that would matter to some folks, of course. If they can't twist simple words, they'll just ignore them.