That 'tunnel vision' disappears pretty quickly if your grandmother walks into the room. I think we make a lot of excuses to ourselves about our ethical behavior in regards to sex. We're not helpless apes at the mercy of our genitals. If we can stop at the crucial moment when grandma walks in we can stop and think about the consequences of unprotected sex, coercing or forcing someone to have sex etc. at any point in the act.