One of those questions we hear over and over again throughout our lives is "Why does sex feel good?" This question has an answer so obvious than one - if that one is inclined towards introspection - must arrive at the conclusion that it is so vapid and so vacuous that it is being asked simply for the sake of its use as a rhetorical device or in order to fill up an otherwise quiet moment during a conversation. The answer, obviously, is "Because if it didn't, it wouldn't happen very often and then the organism in question would go extinct." The thing is, there actually IS another approach which can be taken, and those who were paying attention to the lessons on the topic of sharks, lake ducks and bedbugs have already begun to apprehend it for themselves: It is possible for sex to not only be unpleasant, but SO unpleasant that the female is literally incapacitated and rendered incapable of escaping during the act, thus ensuring the success of the act. One assumes that it remains pleasant for the male of the species in question, of course, but perhaps it's best not to contemplate too deeply what sort of emotional content this has for them.
There is one creature, however, that takes this to extravagant new heights, and which puts to shame the paltry lengths these mere pretenders go to to secure the affections of their respective ladies fair. I speak of the otherwise-unremarkable Callosobruchus maculates Seed Beetle, which unambiguously contains one of...
Behold the physical act of love. See the male's gentle yet determined embrace. See the female's reluctant stance, her vigrous attempt to dislodge her suitor from her anatomy by means of frantic kicking motions with her hind legs. See the extent to which this has any evident impact upon the male's posture and the disposition of his penis. And then, once you feel you have had enough pleasant dreams for one lifetime and are prepared for a lifetime of secret dread and skin-crawling horror, see what exactly it is that has the female so negatively disposed towards her mate's amorous intentions:
Impressive, is it not? This... this is a truly manly penis. A warrior's penis. A penis one could proudly wield in battle as he caves in the skulls and pierces the armor of his foes with it. By comparison, the human penis seems almost womanly in its gentle curves and rounded edges. Does it not seem, gentlemen, that you are in some sense of the words emasculated by the sight of so manifestly awesome a dong?
It seems, in some sense of the words, that this mighty morningstar-styled phallus is wasted on an organism whose mind is too simple to appreciate the aesthetic perfection of what natural selection has wrought in them. Plainly, we, as humans, have gone critically wrong in our evolutionary path, if there was some other path which could have led us to this destination. HOW COULD WE HAVE BEEN SO BLIND?
And behold here: See this arrangement, which seems so like a combination of all of the best and most manly traits of a garbage truck, a vice grip and a bear trap? It does EXACTLY what you think it does, and it does so with a magnificent gusto. How many times, men, have you been with a woman and thought to yourself "The only thing that could make this better is if I had a giant set of claws on the underside of my manhood that could reach out and just GRAB the inside of this fine gal, gnashing and crushing her lady-parts in it horrific, barbed grip so that she couldn't possibly escape from my loving embrace"? Well let me tell you something, buddy: The Seed Beetle male has never needed to HAVE that thought. Or any other thought. Because it's a bug. And they don't think. Probably.
But that's beside the point. The point here is that what we have here is an alternate answer - and perhaps a more compelling one for those "visual learners" among us - to the question of why sex feels good. The answer is "Because if we can't have penises which look like someone welded together a week's worth of floor scraps and broken machines from a particularly imprecisely-run factory, then we'd better fucking well make it feel good, 'cause otherwise, we've got NOTHING, that's why."