You're answering a question other than the one I asked...
I was answering on the secular challenge. It begins with the founding principle. Otherwise you aren't really asking anything more than can a social order found itself on rational principles at odds with our own. Of course, because it can then define its own terms.
...Even our society recognizes that it is permissible to kill someone other than in strict self defense. Consider the death penalty.
Most rules have at least the appearance of an exception while remaining what they are. Some jurisdictions allow for and other's deny the death penalty. The larger compact permits it within strict boundaries. Those boundaries are that the administration cannot be cruel and unusual, meaning the punishment cannot permit torture and/or deliberately degrading punishment.
Among the arguments from necessity that make for the DP exception is that someone who has taken from another that foundational right to be cannot be entrusted with his own life for fear of compounding the act. Or, in essence, an extension of the argument for self-defense as extrapolated to include others.
I don't even think it's permissible to intend to kill someone in self defense, at least, qua private individual.
It is absent your ability to disable with sufficient certainty of protecting your life. And that's a hard call for anyone to make without an inordinate skill level in administering violence, even with calm and time, neither of which tend to be present in the act and moment.
My question is whether the State can "deputize," so to speak, by law the offended spouse to exact due vengeance.
I'd say, without even approaching the penalty, that it would be an easy thing to argue against, making a party to an action, essentially, a judge in the matter. Most professions recognize the problem of even positive emotional entanglements and their impact on performance and judgment.
You are likely to keep talking about the "values" our society is based on, but I'd much prefer simply to talk about justice,
That would be a value, shared or not. The rest is just how we reason in support of the value.
i.e., that whereby each is given according to his due, and simply ask whether the woman in question deserves to be beaten, and if she does, whether her desert for a beating rises to the level of "deserves to be beaten to death."
It's just that I quietly enjoy my property and person without unlawful interference. It's just that someone who attempts to abrogate my right be punished. But equating a fiscal or emotional harm with the physical is inherently subjective and arbitrary. It invites disparity and injustice.
If you say "no" then I'll point to the Old Law and ask you why you think Moses legislated unjustly in the case of adultery.
I'm not obliged to judge a man who lived in a time without any number of advantages we enjoy today that could have afforded him a greater freedom in choosing. It's not fair to him and it's not relevant to me.
You'll insist, of course, that you are not "under the law," or whatever it is that protestants insist on repeating.
I'm even less compelled by your Catholic snobbery, by which I mean your and not some inherent Catholic flaw, than I am by the degree which it blinds you, including its impact on your grammar. But no, I am not living under the Mosaic compact. Consider this my answer on part two, omitted.
...If our society didn't follow that principle, and instead decided to punish criminals in a way exactly proportionate to their crime, would that be unjust?
The problem with proportional is that it can't be objectively arrived at outside of the literal. And even that has problems. Is it the money I steal from you or the damages caused by the theft? We attempt to make the punishment fit the crime in terms of the severity of deprivation (time) of rights, but when you seek to move beyond that into some literal approximation it's throwing darts in the dark. That's not really justice.
Is it intrinsically unjust to beat a batterer?
Yes. The easiest illustration would be found in ordering the rape of a rapist. If we find an action so vile that we make it a violation of law then to return the injury with a likened action is to reduce the state, however we justify it, to the same part as the violator. This is another argument against the DP, though as I noted there are more than a few arguments for it that move the boundaries of discussion beyond what we're examining here.
...The marital contract by its very nature implies a right to the person of one's spouse...thus the so called "marital debt," the moral prohibition on adultery, etc
Rather, the marital relationship opens both parties to responsibilities which they may or may not choose to fulfill and which, depending on the nature and weight of those choices, may lead to the abrogation of the contract. So you may have a reasonable expectation of marital relations. You may use the routine denial of that expectation as a foundation for ending the contract, but you at no point are permitted to subjugate her rights as an individual to your own. You are not entitled to violate her because you feel cheated.
...I don't want to talk about rights.
Then you don't really want to talk about the issue, only talk about how you mean to justify what could not be reasonably justified within the context of rights. Why should that interest me? Feel any way you like about it. Determine the rights of your own inner kingdom and predicate them on whatever suits you, so long as you don't attempt to act upon them in relation to another.
Our consciences are our own.
Let us simply talk about "the right." And I'll ask you what is the right, objectively speaking, of a woman who has done the things I've described, who has the kind of character that I have described. But to speak of "the right" for this woman is simply to ask what, objectively speaking, she deserves.
You've stepped into the moral realm, into the real of conscience and my answer is that she deserves what anyone does absent grace. My answer to her would be Christ's answer when those who accused her had fled the field. The rest, the legal portion, I've spoken to in my last.
And I'll answer: "Death."
And there was a man forgiven a great debt, who seeing another who owed him a lesser took that other man and cast him into prison until his debt was paid.
I don't envy your position, Trad. Not the least bit.