A very liberal sexual ethics now holds sway in Western culture, such that mutual consent alone is widely seen as morally legitimizing almost any sexual activity between adults. It is further commonly assumed by both philosophers and nonphilosophers that arguing for some alternative to liberal sexual ethics requires appeal to ethical commands specific to some religious tradition or other. The purpose of this paper is to challenge that assumption by suggesting some purely naturalistic and independently-plausible premises that can be used (...) to argue for a much more conservative system of sexual ethics than is widely accepted today. (shrink)