Andrea Dworkin argued that sexual intercourse between a man and a woman is always wrong because it involves a violation of the woman's bodily integrity. She concluded that until recent advances in medical technology, it was impossible for humans to permissibly reproduce. The antinatalists, on the other hand, continue to hold that it is impossible for humans to permissible reproduce. Such views lead to an incredulous stare. It is very tempting to levy against them an argument like this:
- Coital reproduction is necessary for the minimal flourishing of the human community under normal conditions.
- Whatever is necessary for the minimal flourishing of the human community under normal conditions is sometimes permissible.
- Coital reproduction is sometimes permissible.
Reproduction is not the only case where issues like this come up. For instance, the destruction of non-human organisms, say plants, seems necessary for our flourishing. And I suspect that under normal conditions the killing of non-human animals is necessary, too (if only as a side-effect of plowing fields, say). Taxation may be another interesting example.
I have heard it argued that (2) is in itself a basic moral principle, so that killing non-human animals as a side-effect of vegan farming is permissible because it is permissible to ensure minimal human flourishing. But that seems mistaken. Rather, while (2) is true, it is not a moral principle, but a consequence of a correlation between (a) fundamental facts about what moral duties there are actually are and (b) facts about what is actually needed for minimal human flourishing under normal conditions.
This leads to an interesting and I think somewhat underexplored question: Why are the moral facts and the facts about actual human needs so correlated as to make (2) true?
Theists have an elegant answer to this question: God had very strong moral reason to make humans in such a way that, at least normally, minimal flourishing of the community doesn't require wrong action. Non-theists have other stories to tell. These stories, however, are likely to be piecemeal. For instance, one will give one evolutionary story about why we and our ecosystem evolved in such a way that eating persons wasn't needed for our species' survival, and another about why we evolved in such a way that morally non-degrading sex sufficed for reproduction. But a unified answer is to be preferred over piecemeal answers, especially when the unified answer is compatible with the piecemeal ones and capable of integrating them into a single story. We do, thus, get some evidence for theism here.