There are a lot of great comments; sorry I can't address all of them with the depth I want. Let me first say that I haven't read the Rosen article and don't plan to. I've never found anything he wrote insightful and have usually found it positively misleading.
Mona: thanks for reminding us that Roe *created* the religious right position against abortion. In UK, New Zealand and elsewhere abortion is legalized by *statute* and was the result of surprisingly genuine debate in legislature. (I say "surprisingly" because legislative "debate" unfortunately rarely seems genuine. But its possible as these debates show.) The legislative decisions there are generally seen as legitimate as opposed to Roe for us.
Paige: I agree with you that oppressiveness of a law ought to be sufficient reason to do away with it. When I said "We cannot say an oppressive law ought to be done away with *because it is oppressive*" I meant that *when the judiciary is the final authority on constitutionality*, one (regrettably) can't argue (as one ought to be able to) that a law ought to be done away with simply because it's odious. One (regrettably) has to argue indirectly through precedent, original intent, etc. That means that the result one gets to might not be optimal, and it won't be for the right reasons; and in the future one who wants to change fundamental policy has an incentive to poor time and money into changes judges rather than fellow citizens' minds. That can't be good for the country.
I am glad you mentioned the Hart-Devlin debate. I am a huge fan of Hart's work. (For those interested in a look at that debate, the following entry is a good one. http://plato.stanford.edu/entries/law-limits/ ) I agree with Hart, and with Mill before him, and Kevin's spot-on comment: prevention of harm to others is the only reason for which the state may limit my or your freedom. It is indeed none of the state's business "what herbs I ingest or what I do with my genitalia".
TGGP and Keith: I was interested by the post on rule of law. I have a lot to say about that, which I'll save for another time. I'll make one minor comment now, on Keith's opposition to "legal positivism". Watch out for that term–it's one of abuse in libertarian circles. The "legal positivism" of the sort Walter Block, Randy Barnett, etc. denounce has nothing to do with the actual view "legal positivism" which is in no way antithetical to a libertarian worldview. For actual *legal positivism* see the extraordinarily informative http://plato.stanford.edu/entries/legal-positivism/ . (While I'm on it: Block's and Barnett's culpable and chronic misrepresentation of legal positivism is really inexcusable. It sends the message that libertarians aren't interested in actually learning what its perceived opponents actually think.) I gather your opposition is to a view of the following sort. "Law qua law is legitimate and ought to be obeyed by citizens." Of course that view ought to be rejected. It's not "legal positivism," which is merely the view that identification of the existence and content of a law can be made without recourse to moral considerations.
Keith: Your assertions that the Constitution is dead letter and that legalism leads to Nazism are absurd. With respect to the first one: Whether or not the current government resembles *your reading* of "the original structure of government outlined in the Constitution", the terms of the Constitution frame the debates that take place in government. A judge cannot decide a constitutional case without at least paying lip service to the Constitution–and that need to justify one's decisions in public in terms of agreed-upon language counts for a lot. (I know that on your "realist" view of law and legal process, lip service and window dressing is all there is. I don't deny that some, perhaps many judgments, feature some, perhaps a lot of post hoc window dressing. But there are also officials who sincerely take themselves to be in the public service; deciding as they sincerely think is best for all of us.) Your second claim is simply idiotic and I'm somewhat ashamed to take it seriously enough to respond. Let me just say that Nazism is seen by those who value "rule of law" as the antithesis of the latter ideal. Is legalism compatible with evil? Of course. Does it inevitably lead to evil? Of course not.