Over at Balkinization, Michael Stokes Paulsen imagines what a five-justice majority of the Supreme Court (Kennedy, Souter, Breyer, Ginsburg, and Clinton) might say in striking down anti-prostitution laws in the 2010 case of Spitzer v. United States:
There is no persuasive basis for distinguishing the Lawrence Liberty here. Moral condemnation is not, as we have shown, a persuasive or legitimate basis for laws interfering with intimate sexual liberty. Again, in Lawrence, we observed (following JUSTICE STEVENS's dissent in Bowers), that "'the fact that the governing majority in a State has traditionally viewed a particular practice as immoral is not a sufficient reason for upholding a law prohibiting the practice.'" , Slip Op. at 17. Nor is the fact that the arrangement may have a commercial element sufficient to distinguish this case. Abortion, which we have held to be an essential aspect of liberty, usually involves a commercial transaction. That does not lessen the liberty-refuge that we think should not be doubted.
I can't claim to know anything about prostitution jurisprudence. But setting aside the question of whether the commercial nature of prostitution distinguishes it significantly from consensual sodomy, it seems to me that "moral condemnation" is not the only justification a state could offer for anti-prostitution laws. Unlike in the case of sodomy, legalized prostitution pretty clearly contributes to a number of tangible social ills the state has an undisputed interest in preventing--see Brad and Nick Kristof on this point. Surely that would be sufficient to pass the rational basis test, no?