In the contraceptive era, however, that dynamic has been reversed because contraception has made sexual access virtually universal. Men have little incentive to marry, rear children, or develop responsibility. Their competitive urges, instead of being directed toward marriage and family, are directed toward competition and violence. But here I depart from Freud, and I wonder whether sexual behavior, like aggressive behavior, increases in a damaging way with greater expression (a phenomenon known as the "catharsis hypothesis" or "ventilationist hypothesis," both of which suggest that just "letting it out" is a good thing). If that is true, then the greater opportunity for sex guaranteed by contraception may in fact be feeding a cycle that is ultimately destructive for individuals and society as a whole.

The more we understand brain chemistry, the more we understand the biological and psychological mechanisms of sexual attraction and attachment. Primarily, we have come to understand more and more about the limbic system of the brain. We know there's a primitive, mammalian reward center that is lit up by sexual stimuli. For example, it appears that in men the visual stimulus of seeing a sexualized image of a woman is similar to the stimulus produced by inanimate objects, suggesting that one form of sexual discrimination might be biologically rooted. Moreover, men are particularly susceptible to falling into patterns of addiction around sex, and the pattern of addictive behavior is common. Craving creates amplified desire for the object, which leads to a vicious circle of amped-up desire/temporary satisfaction/greater desire/need for more and more of the object.

To put it most starkly: widespread use of contraception has made sex cheap and abundant. It has generated risk-compensation behavior, which has further generated competition and envy between men, between women, and between men and women. The resulting sexual behavior has fed addiction to sex among many people (especially predatory men), in some cases an addiction more powerful than cocaine.

There is a mathematical logic to the reality that has unfolded because of widespread social acceptance of contraception. Let's imagine that before the McDonaldization of sex, when sex carried the risk of pregnancy, those who risked most—women—were likely to be careful about the circumstances leading to sex. In short, the number of sexual encounters was likely to be low compared to today. Let's also imagine that because there was little effective contraception, the percentage of sexual encounters that led to pregnancy (fecundity) was higher.

Before widespread contraception, then, let's imagine:

30% of the number of sexual encounters (say, 1000) led to fecundity = 300.

After widespread contraception, leading to cheaper and more widely available sex, the result would look something like this:

5% of the number of sexual encounters (now 10,000) led to fecundity = 500.

In short, widespread contraception reduces the percentage of fecund sexual encounters, but because of risk compensation the total number of fecund encounters actually rises. And since many of those fecundities are unplanned, abortion is often the next recourse.