Sex is the root of many of the social ills that plague our country. The government has a legitimate interest in curtailing those social ills by regulating the sexual activities of residents. Widespread, indiscriminate regulation of bedroom activities seems rationally related to legitimate government interests.
Accordingly, there ought to be a law that prohibits sexual relations in the absence of a license issued solely to couples actively seeking to conceive a child (providing they qualify to receive their child-bearing license, of course) and only if done in the missionary position. All other sexual positions are lewd and lascivious--and we all know that the government has the police power to criminalize lewd and lascivious conduct in accordance with the moral disapproval of the religious folk.
After all, the Constitution doesn't prohibit the government from regulating our liberty interests (which does not include a right to privacy, according to "strict constructionists") so long as we're provided due process of law.