Sexual Morality and Collectively Harmful Practices

Jason Brennan famously argues that the politically uninformed have a moral obligation not to vote. One of his arguments for this claim goes as follows (2011, 71):

1. One has an obligation not to engage in collectively harmful activities when refraining from such activities does not impose significant personal costs.
2. To cast an unexcused harmful vote is to engage in a collectively harmful activity, while abstaining imposes low personal costs.
3. Therefore, one should not cast an unexcused harmful vote.

Brennan defines a "collectively harmful activity" (CHA) as "a harmful activity caused by a group or collective, where individual inputs into the harmful action are negligible. [...] For instance, producing air pollution is a collectively harmful activity. As a group we do a lot of damage, but as individual polluters we do negligible harm" (ibid., 71).

Now, it is highly plausible that premarital sex qualifies as a CHA: it leads to out-of-wedlock pregnancy (thereby contributing to poverty, crime, and abortion), as well as being correlated with higher rates of divorce and infidelity and lower levels of marital happiness. Given that higher rates of social disorder and a weakening of the married family constitute significant societal harms, it seems that Brennan's argument against uninformed voting will also apply to premarital sex.

It is important to note that given Brennan's definition of a CHA, it is not necessary to show that every act of premarital sex leads to the aforementioned harmful consequences, or even that most such acts do so: the relevant thing is just that the widespread practice of premarital sex in general constitutes a CHA (in virtue of its harmful effects on society and the married family). Given that this is so, it follows from premise (1) of Brennan's argument that there is an obligation to avoid premarital sex when doing so does not impose significant personal costs (i.e. always or nearly-always).

This argument is very similar to one given by Alexander Pruss. In his book One Body, Pruss writes:

The significant number of children born outside of marriage in this country might arguably be a major contributor to poverty, poorer moral education, and other social ills. By engaging in premarital sex, one takes the risk of being a contributor to this serious social problem. It is true that, more likely than not, procreation will not happen in any given act. However, a significant number of children born outside of marriage are conceived despite the use of contraception. Thus, even engaging in contraceptive intercourse, one is risking being a contributor to the problem. And there one is at least presumptively doing wrong. (2013, 187)

Brennan’s principle concerning collectively harmful activities provides a useful way of precisifying this argument. It also provides a way of extending the argument beyond premarital sex to include other potentially wrongful behaviors. The use of pornography is a very plausible candidate: the porn industry is utterly rife with abuse and trafficking, and its proliferation has plausibly contributed to the general loosening of sexual morals in our society (which in turn makes it a contributor to the premarital sex problem). Furthermore, pornography use is correlated with lower levels of relationship satisfaction. Given all of this, it very plausibly constitutes a CHA. Since refraining from pornography use carries no significant personal costs, it follows that there is a moral obligation not to use pornography.

For theists, there is another potential dimension to this argument: even if one does not think that the aforementioned considerations suffice to show the intrinsic wrongness of non-marital sexual activity, they plausibly do suffice to give God very strong reason to prohibit such activity. This fits nicely with the accounts of Christian sexual morality given by e.g. Murphy (2002) and Swinburne (2007).

There are very probably other activities to which one could apply a very similar argument. Hard drug use comes immediately to mind.