Mens Rea (guilty mind) is only half the explanation. Why should a pregnant woman not have mens rea? Anyone looking for clean, crisp answers here is out of luck unless you choose to apply nothing but the most simplistic religious doctrines. Any look at history, psychology or biology is going to be a venture into muddy waters.
First, let's look at the crime of reckless endangerment: it doesn't apply to what I do to myself. As a snow skier I recklessly endangered myself a hundred times a day. It's allowed. If I had placed someone else at the same risk against their will I'd have been guilty. Part of the answer about abortion vs. feticide is the half-true statement that the fetus
is the mother in the eyes of the law just as my leg was me when I risked breaking it while skiing. The woman choosing an abortion is -
in her mind - dealing with her own unitary biology. The attacker who, with intent, tries to end the viability of as fetus against the mother's will, however, is treating the fetus as a separate being. (This assumes feticide requires intent and mens rea, which ought to be the case.)
Now that's a very unsatisfying answer for a couple of reasons. There's no single good and complete answer.
Another half-true explanation is to say that the fetus enjoys identical status as a person in both cases, but that in the case of abortion the personhood of the fetus -- the rights and protections that attend personhood -- is trumped by the special privileges enjoyed by a woman in the process of reproducing. She's
allowed to end the life of the fetus
despite the fetus's being a person. The guilt in her mind is, in this special circumstance, something reserved for individual conscience and outside the purview of criminal law. But an outsider has no such privileges (unless a licensed medical pro and the woman is unconscious and the pregnancy is an immediate threat to her life etc.). Why should this be so? Answering that would require an essay. Answer it for yourself, and if you have no answers you're probably "pro-life". If that's the case, I ask only that you recognize that other people do have answers with which they're at least half-satisfied.
Finally, one could argue that the fetus is not a person (at least in the first two trimesters) but that the special circumstance means we should treat it
as if it were one in the case of intentional third-party feticide. While not a person, the fetus is clearly a potential person, and violently ending the potential is, in the eyes of the law, equivalent to ending life itself. To the mother, the potential is
only potential. She is the life and the fetus is basically the same as an egg. But to the state that egg-like mass, at least at the point it becomes viable outside the womb, has person-like value. See the
state laws and note how in many cases the fetus must be "quick" or viable for the law to apply.
Paradox? Ambiguity? A lack of consistency? Yes. Absurdity? Irrationality? Senselessness? No. This is one of the few situations where that can be true. Enjoy the experience.
PS: If the criminal did not know the woman was pregnant, typically the crime is not relevant - see those state laws.
PPS: Bbauska stated that he intended "to show the hypocrisy in the government's position." There's no such thing as "the government's position". That apostrophe needs to be after the pluralizing "s" because we're talking about fifty different governments (except in the minority of cases where the federal Unborn Victims of Violence Act of 2004 applies).