My point was that this merely shifted the ground of debate. People began saying that blacks, women, etc. were "not really human" or "sub-human". Today there are those who think fetuses have the same moral rights as babies, and those who say fetuses are not "really human [individuals]". And so on.

In other words, it's a game of definitions and reference class tennis. You should taboo "members of H. Sapiens Sapiens" and specify how you really assign moral value to someone. Your definition should also work with outright non-, pre- and post-humans too, unless you're willing to say outright that anyone who can't breed with today's humans necessarily has zero moral worth.