Unborn Victims, II
Here's the Act. It makes the "killing" or injuring of an unborn fetus a separate offense to the attack on a pregnant woman. The law is an alternative to what many states have here--which is an increased punishment when the carried fetus is injured or "killed." Here's relevant portions:

Sec. 1841. Protection of unborn children

(a)(1) Whoever engages in conduct that violates any of the provisions of law listed in subsection (b) and thereby causes the death of, or bodily injury (as defined in section 1365) to, a child, who is in utero at the time the conduct takes place, is guilty of a separate offense under this section.
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(C) If the person engaging in the conduct thereby intentionally kills or attempts to kill the unborn child, that person shall instead of being punished under subparagraph (A), be punished as provided under sections 1111, 1112, and 1113 of this title for intentionally killing or attempting to kill a human being.
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(c) Nothing in this section shall be construed to permit the prosecution--

(1) of any person for conduct relating to an abortion for which the consent of the pregnant woman, or a person authorized by law to act on her behalf, has been obtained or for which such consent is implied by law;

(2) of any person for any medical treatment of the pregnant woman or her unborn child; or

(3) of any woman with respect to her unborn child.

(d) As used in this section, the term `unborn child' means a child in utero, and the term `child in utero' or `child, who is in utero' means a member of the species homo sapiens, at any stage of development, who is carried in the womb.'.

A woman carrying a fetus might well regard that fetus as a human life. A couple might also regard the fetus as a potential child, and that potentiality is destroyed by the attack on the woman. In these respects, I have great sympathy for laws increasing the punishment for assaults on women when pregnant. Further, where the harm to fetus is involuntary, I do not see clearly see why Congress can't take a stand as they've done here. The two pieces of this legislation that flash warning signs to pro-choice folks are these: 1) that the crime is a separate offense and 2) the legislation defines the embryo as a human being. I don't think the concerns will amount to anything damaging to a couple's right to abort a fetus.
1) that this is a separate offense is more rhetoric than substantial change in law. sure, the rhetoric might find use in pro-life arguments; but it is undeniable that harm to fetus is, in fact, a separate offense. Again, even where the carrying woman does not regard the fetus as a life yet, it is surely a potential life--beyond the far less potential of pre-fertilization. Thus, if the woman is shot in the arm, then in the gut, she is harmed and the fetus is harmed. Whether we think of that fetus as a part of her or a separate being does not really effect whether the harms are separate.
2) rather, the more legitimate danger symbol to pro-choicers is the defining of embryo, or "child, who is in utero" as "a member of the species homo sapiens, at any stage of development, who is carried in the womb." (emphasis mine).
Here, Congress is defining life, I think. They are making a powerful decision for me- and one that is central to my being pro-choice; to wit, that the fetus is not a human that can be killed. In this regard, the danger to choice is more potent...but still limited to rhetoric. That definition of a child in utero is limited to this Act. In other words, it merely explains why this is a separate offense as opposed to increasing the penalty for assaults against pregnant women.
Again, I think I am fine with this. As many members in Congress and many Americans indeed believe the fetus is a human, I can't well prevent legislation so saying. But, of course, we will have to see whether and how this comes into play in shaping the privacy/abortion rights set out in Roe and Casey.
But that last point is key. Abortion is a right- in that the Court has said the government cannot intrude upon the private decision involved in abortion. In my mind, though it may be different to Blackmun, Douglas et al, this privacy involves the tremendous decision regarding what is life. The Court is there to protect that private decision making. This Act does not intrude upon that decision, though it may put a public/government endorsement on the fetus=human choice. Pro-choicers, though, can't argue the Establishment Clause goes so far.

Tangential:
Anti-abortion folks make an impressive argument: why does the Court allow people to define life in the abortion context? What if it allowed murder to excape conviction because the murderer did not regard the victim as a person? If I think abortion is murder, how can I not be appalled that my government stands by and allows it?

The last point is perfectly sound, but not the first two. If you are pro-life, you must be appalled at our Court decisions allowing abortion- just as others have been appalled at government decisions contrary to their views...from Miranda rights to greater leniency to police procedure.

As to the notion that abortion is this strange area where the Court allows people to decide life and death: in a sense, this is so- and rightfully so. While person A may be certain the fetus is a living human, person B thinks it is not. But instead of arguing the same old bit about choice in this matter belonging to the couple, let me make this point: the Court does allow, in a typical murder context, someone that does not think the victim is human to escape the same punishment of someone that does so regard the victim as human. along with other routes, this is called the insanity defense.
To be guilty of a crime, you must have both 1) done the act and 2) had the mental culpability to acheive the act. If X shoots Y, knowing that he shoots Y, and knowing Y is a person...X might be convicted of 1st degree. But if the defense can show X did not have any idea Y was a person (X has a mental disability that sends him into strange sleep-walking spells; or, as in Chapel Hill a decade ago...X is schizophenic), then X does not have the mens rea, or moral culpability element of the crime. But largely, society has deemed every sane human with the knowledge that other people are fellow humans. We thus assume a moral culpability when you kill another human.
In the abortion context, society does not deem it insanity to not regard the fetus as a human. But the mens rea (culpability) is similarly not there where the couple does not regard the fetus as human.
Of course, this argument is problematic on numerous fronts. What if the couple does think the fetus is a human? Can they be prosecuted? But this it not supposed to be a way to argue for abortion if the right is taken away. Whether, it is to point out that society, and the courts, do allow some space, albeit very small, for this notion of defining personhood.