Is the teacher telling them to have sex whomever?

Not exactly. The instructor was explaining that a men has two type of mana and with the help of women (by succumbing to intercourse) could help convert the explosive mana, uncontrollable ("estra" - thats what they call it) to a stable and controllable mana ("intra"). So, having s** with them helps men in converting the two.... Correct me if not...