It's not a completely rational choice. Sexual relationships tend to lead to emotional attachment. So you start sleeping with someone because they're hot, even t

It's not a completely rational choice. Sexual relationships tend to lead to emotional attachment. So you start sleeping with someone because they're hot, even though they are a poor prospect for marriage, but you end up falling in love with them anyway. One thing leads to another and suddenly you're married with kids. Some people are capable of exceptional rationality—or perhaps exceptional coldness and calculation—but most of us are merely middling in our capacity to act contrary to our emotional natures. So we do better by avoiding reckless sexual relationships in the first place. Of course, that is itself a feat of rationality over human nature, so maybe we should organize our society to guide us to the right decisions. This is why one might rationally want socially conservative laws and institutions.