As far as the death penalty, the key distinction here is that the unborn haven't committed a capital crime. When someone commits a crime, they merit or deserve punishment, and I do think some crimes rise to the level such that the death penalty is an appropriate response by the state. I think a similar argument can be made with respect to self-defense that people who unjustly attack you or your family forfeit their right to life - and furthermore, this asymmetry I pointed out earlier (personal freedom vs. life in case of abortion) doesn't apply so much when your own life is in grave danger. I do think war is your strongest argument here and I don't have a simple answer, since wars are fought for so many different reasons, but I do think that similar to self-defense of a person, nations have a right to defend themselves against unjust aggressors. Of course, defining this and determining when circumstances truly justify war is much easier said than done.
OK - my argument here might be phrased poorly as I'm thinking it out as I write it.
Why do we make these things illegal? Is it not because in some way they pose a difficulty to society or individuals; it is difficult to live peacefully if people can go around murdering or looting, and so on; at its heart a utilitarian argument about how best to "order" society. Can not the same principle apply to abortion - the burden that an unwanted - and perhaps unloved - child places on society and its parents? This sounds a little callous and perhaps it is; but it seems to me that it is the logical extension of the same idea.
If the right to life is "fundamental" as you say, how can it be abjured by committing a capital crime?
I would largely agree that we make things illegal because they are in some way destructive to society, albeit with some disagreement on the principle being fundamentally utilitarian. I would hold that what is or is not destructive is not ultimately a function of our experience of pleasure but in our fidelity to natural law, ie. the moral code written upon every human heart. Of course when the question is illegality, there are practical considerations that are also important. For instance, lying cannot really be banned.
In the case of capital punishment (which btw I don't actually support being used in the US), the argument is not that society is better off without the person but that that person's crimes are evil enough that they merit the government executing them. From a purely utilitarian perspective, we probably "should" be executing a lot more people, many of them now having committed any serious crimes, eg homeless people, handicapped people, etc. There are of course utilitarian arguments about the pleasure and enjoyment of those people who otherwise might be executed need to be taken into more consideration than the pleasure removed from others. I think through this lens, we should conclude that the pleasure the fetus would experience throughout his or her entire life also should be taken into consideration, such as we would for an unwanted child that has already been born. From a purely utilitarian perspective, I'm not sure I see why they would be treated that much differently (minus the effects of short term loss of enjoyment during the pregnancy itself the equation basically balances the same).
Now, I'm not a utilitarian and don't view pleasure as the highest good, nor do I think laws should be ultimately based on such even if they take into consideration how actions hurt others. My belief is that it is wrong to actively kill a fetus on natural law grounds just as it is to kill anyone else. And while political realities prevent that from being enshrined in law with absolute logical consistency, I do think it should at very least be illegal under most circumstances. There are so edge cases where I recognize even if abortion were to be outlawed in general, it would almost certainly still be permitted.
