I think that if you murder a woman who is pregnant, the death of the fetus should be considered manslaughter, since there was no pre-meditation in the killing of the fetus.

But since the fetus died as the result of a felony, as opposed to the private rights of parents, that it should be a crime IF the woman is more than six months pregnant, thereby validating the fetus as a viable embryo.

Having the double-murder law is useful in that it protects both the mother and pregnancy, in cases where the husband/father would kill the woman who is pregnant, like Scott Peterson did, to get rid of a future he didn't want.

That law recognizes that sometimes a woman is a target for attack simply because she is pregnant.