Quote: Uschi said: To take this further from this mathematical-esque depiction, when the person B gets to know each person X before coming into sexual contact with them, the chance of contracting a deadly AIDS is minimised. The promiscuous populations A and N and Q are at higher risk because they allow themselves to be prey for creepy lechers who contract STDs/AIDS and don't care if they pass it on.
You're prematurely assuming that B knows how much knowledge to encompass from his sexual partners before proceeding with intercourse.