You misunderstand the Sex Positive Agenda. It seeks to encourage an active sex life at all ages. Not necessarily intercourse but whatever sex acts you want to engage in (with a partner of either sex, animal, or relative; there are no moral offenses in the Sex Positive world; although rape is frowned upon, rape fantasies are "okay").
It is one thing to say "if they are going to engage in it", it is quite another to tell kids "you should engage in it...".