A. A (rare) commenter asked for an opinion on this post on a blog I had honestly never read before. The post contains a critique of a kind of argument against sodomy not uncommon in conservative circles, embedded in a sarcastic argument against procreation. So here we go...
B. The argument goes like this: X causes discomfort or involves violence (taken broadly), therefore God doesn't will X, therefore X is morally offensive.
C. Obviously this kind of reasoning doesn't hold. It doesn't hold for arguments against sodomy and it certainly doesn't hold for arguments against procreation. Life is difficult and more often than not the better path, the more virtuous path, will demand a degree of suffering and violence (again, in a broad sense). It is painful for me to get up at 5am. It is painful for me to study hard and think through things diligently. It is painful to raise children and care for them and educate them properly. In all of these things there is some concomitant good which justifies our action. In child rearing, the good is that of our progeny, which (because we love them) pleases us. In more day to day virtues (waking early, working diligently, etc.), the good is whatever end we're striving for. Etc. Now, because the development of virtue involves a kind of suffering, the lower pleasures are frequently obstacles to virtue. Some days I sleep in; some days I browse the internet for hours or just eat and watch movies. The pleasures involved in these activities appeal to the untrained (unvirtuous) mind as a surer good than the higher goods which can only be obtained through virtue (and the suffering involved in forgoing lower pleasures). But it is necessary to act against our lower appetites if we are ever to do anything of worth whatsoever. Likewise, the craftsman must be prepared to endure a certain measure of failure and pain when he is developing his art. Anyone who has ever built anything or even cooked anything knows how true this is.
D. Aside from that, one problem I see with the usual "evident telos" approach to arguing against sodomy is that many parts of the body have multiple "evident tele". Mouths are for eating and drinking, breathing, speaking, gum chewing, and sometimes kissing. With such a diverse set of ends, the mouth seems to function as merely a tool in service of whatever we're trying to do. Why shouldn't genital organs work the same way? I've thought some about this problem, and I think the answer isn't likely to come by way of arguing specifically about unnatural sexual acts, but by way of a broader consideration of human nature, the relationship between body and soul, divine providence as evident through reason, and the structure (which would, presumably, reveal itself to be a pathology) of unnatural sexual desire. Obviously, George, Finnis, Boyle and company have ready answers to these problems, but I haven't read them and am inclined to distrust them.