If the woman wanted to excise a cyst, you’d be absolutely right. But since what we’re talking about is the intentional killing of an innocent human being (who is incontrovertedly not a body part, but a distinct human being, with different DNA than the mother), your analogy is inapposite. A better analogy would be a landlord who locked a tenant in the building and set it on fire with the intent of killing the tenant.
incontrovertedly = incontrovertibly