Probably, he is going to use the "men are biologically programmed to spread their seed." That is not untrue, however, human beings are not like the other animals in that we have intelligence and more emotional attachments to our human companions in MOST instances, at least those where you care for and love your human partner.
I think some people have just never experienced love, and so they don't have any idea how it is when you have "strong" feelings for another person. I'm not claiming that there is only ONE person for every person of course, or that there won't be temptation, but the point is, if you really love and care for the person you are with you would not want to hurt that person and would avoid doing that if at all possible. This is just my opinion, of course.