Decriminalized my foot - prostitution and solicitation are constitutional rights, found in the same place one finds the constitutional right to homosexual marriage.
Nobody's arguing about the constitutionality of it: Neither "rights" are in the Constitution, so states have the power to legalize and regulate or ban them as they see fit.
I know you're being sarcastic, but you make a good point. If abortion is Constitutionally protected under some vague "right to privacy", and sodomy is protected under the same principle, then whatever two consenting adults do in the bedroom should also be protected, even if cash changes hands.