When she was a law professor at Columbia, she, Brenda Feigen-Fasteau, former director of the ACLU's Women's Rights Project, and 15 law students put together a report for the U.S. Commission on Civil Rights. The report, released in 1977, gave as one of its "Recommendations" (p. 102):
18 U.S.C. §2032 — Eliminate the phrase "carnal knowledge of any female, not his wife who has not attained the age of sixteen years" and substitute a Federal, sex-neutral definition of the offense patterned after S. 1400 §1633: A person is guilty of an offense if he engages in a sexual act with another person, not his spouse, and (1) compels the other person to participate: (A) by force or (B) by threatening or placing the other person in fear that any person will imminently be subjected to death, serious bodily injury, or kidnapping; (2) has substantially impaired the other person's power to appraise or control the conduct by administering or employing a drug or intoxicant without the knowledge or against the will of such other person, or by other means; or (3) the other person is, in fact, less than 12 years old.
The report also said (p. 97) that "Prostitution, as a consensual act between adults, is arguably within the zone of privacy protected by recent constitutional decisions" (citing the right-of-privacy cases), and urged that various federal prostitution statutes be "[r]epeal[ed]." This isn't precisely the same as saying that "there's a constitutional right to prostitution," because of the qualifier "arguably," but it's not that far off; the report wasn't merely impartially noting that this is one possible position, but seemingly endorsing it as the sounder position.
http://www.volokh.com/archives/archive_2005_09_18-2005_09_24.shtmI'm sure the report is widely available. It's been cited many times.