First, joining the Convention makes sense in a conventional national interests analysis. America's failure to join will cost it more than signing on. There is already a drumbeat on the subject: US nonparticipation is a boilerplate punchline among international actors critiquing US human rights practice. That doesn't present a direct harm to US national security (in, say, the way that Guantanamo has), but it nibbles away at the national interest. Given the small cost of participation (especially as conditioned by some reasonable package of reservations and understandings), ratifying the treaty looks the preferred, rational choice.
But even if we don't sign on, the convention's substantive terms will insinuate themselves into US practice. Eugene assumes that the US can say no to the CRC, that America can insulate itself from universal international practice (to anticipate Ken's objection here, universal at some core discursive level even if many other countries have attached significant reservations to their ratification). I don't think so. There are too many entry points for international law, including through state governments, nonstate actors, and the courts.
Take the CRC provision barring life sentences for juvenile offenders, among those which Eugene finds objectionable. I'd be willing to make a small bet that within the next 20-25 years that practice is halted in the US, whether or not we formally join the CRC. It might be the courts that put a stop to it, a la Roper. It might be state governments that come around on their own, in the face of ramped-up international static. Nonstate actors (including academics) will be a part of the picture. In any event, the international norm will be a driver. That is, the fact that international law has moved to ban the practice will be consequential, policy aspects of the question aside. That's something that international law skeptics have trouble understanding: the material power of international law.
Now, as I argued in my original post, I find the "foreigners dislike us for our not signing the Convention" argument to be unpersuasive. In principle, I'm fine with doing (cheap) things to produce foreign goodwill that might eventually translate into material benefit for us. I'm just skeptical that the sorts of "international actors critiquing US human rights practice" to whom our nonparticipation in the Convention is "a boiler punchline" will really change their views about us if we ratify in the Convention; and I'm also skeptical (though more tentatively) that those listening to them will change their views about us.
But Prof. Spiro's post also identifies -- perhaps inadvertently -- why signing the Convention might not be cheap. Displeased as I am with the Convention, I'm much more hostile to other aspects of "international practice," such as the norm that governments must suppress so-called "hate speech," the norm of not protecting an individual right to bear arms, and the norm that governments must suppress certain kinds of anti-religious speech (a norm that is not yet entrenched but that some are trying to create). Yet Prof. Spiro has long argued that such norms are likely to insinuate themselves into American constitutional law, even to the point of leading courts to take a more restrictive view of the First Amendment. And even in the post I quote above, Prof. Spiro has likewise argued that foreign norms are likely to insinuate themselves into American law, even if we don't ratify the Convention.
What can people like me, who like American free speech rules, American right to bear arms rules, and the like do to prevent such erosions of our rights? Well, note that Prof. Spiro's claim that "even if we don't sign on, the convention's substantive terms will insinuate themselves into US practice" isn't a matter of some ineluctable physical law. Rather, it's an artifact of domestic opinion. "International practice" is influential to the extent that it has a high reputation among American decisionmakers, perhaps because they see Americans generally as approving of the influence of international practice. It is much less influential if it is broadly condemned as illegitimate by Americans.
If we accept that we should conform with "international practice," then we'll conform; or if our presumption with regard to "international static" is to change our understanding of human rights and proper legal rules, then we'll change them. But if we broadly adopt a view that our rights are a matter for us, and that we should bristle at foreign attempts to impose foreign "practice" rather than feeling cowed by such attempts, then our legal rules are more likely to be preserved in the state that we as Americans would like them to be without regard to foreign pressure.
Now one possible reaction, of course, might be to pick and choose -- to subscribe to those treaties that we like but not the ones we dislike, to take seriously "international practice" arguments but to reject those we disapprove of, and so on. But as I read Prof. Spiro's argument, such a nuanced response will fail: Even if we consider a proposed treaty and reject it, its "substantive terms will insinuate themselves into US practice" despite our rejection. That's true as to the Convention on the Rights of the Child. It would presumably be similarly true as to international conventions that demand the punishment of so-called "hate speech," or of harsh criticism of religions. We can try to pick and choose, but those that we've chosen to reject will still "insinuate themselves" into our law.
It seems then that the one reaction that will most diminish the chance of rejected rules' "insinuat[ing] themselves" is a thoroughgoing condemnation of the influence of the relevance of international practice, and of the legitimacy of allowing such practice to influence our practice. If case-by-case attention to international norms won't be enough to block those norms that we rejected, then it seems to me that only a broad hostility to international norms will suffice.
So if Prof. Spiro is right about the power of rejected treaties to "insinuate themselves" -- a big "if," I realize -- then I think those of us who deeply oppose some international norms (I mention again the norm of compulsory suppression of so-called "hate speech") need to reject many treaties simply for the sake of rejecting the treaties, so at to better create a culture in which international norms have the least chance of insinuating themselves. Every such treaty that's rejected will help reinforce the protection that our law offers to the independence of our own domestic legal tradition.
To be sure, such rejectionism may sometimes be too costly. If we have something serious and likely to gain from accepting a particular treaty, we should be open to that benefit. But we should recognize that there's always a cost, even of a treaty whose terms are by themselves unobjectionable: the risk that endorsing such treaties (and especially "human rights" treaties) will promote a legal culture supporting the erosion of American legal principles that go against "international practice."
(Of course, to the extent that some people find that they agree more with the "human rights" norms of Europeans than of Americans, they may welcome the replacement of American human rights norms in America with more European norms. I write this post, though, from the perspective of someone who prefers American human rights norms, imperfect as they are, over European norms, and who wants to maximize American flexibility to maintain those norms.)