Hearts pump blood, and that is almost all they are good for. That was discovered only recently, and only in one culture, but is true of all human beings thruout the ages. Consequently, the criteria for a good heart are pretty straightforward. If the valves leak, or the muscles contract in the wrong order, physicians are entitled to give those conditions long, nasty names and do what they can to remedy them.
It is true that hearts have another use: they reveal to each of us, and to others who have gotten close enough, something of our emotional state. People used to believe that that meant the heart produced the emotions, and metaphors based on that belief (and more vaguely on the position of the heart within the body) are still common: We say "broken-hearted" and "put your heart into it" and
I put my hand upon my heart
And swore that we would never part.
I wonder what I should have said
If I had put it on my head.
However, few people these days take such talk literally; everybody knows that emotion as well as intellect is mostly in the brain, and that the two are intimately mixed. Awareness of heartbeats is not of great importance in civilized life. If a patient is given an artificial heart that pumps blood quietly, sensible people do not regard the cure as incomplete.
Human feet are mostly used for walking & running, and can mostly be judged by their effectiveness for those purposes. In that respect they are almost like hearts, tho their design is not nearly so well perfected, probably because they came much later in our natural history. Feet, however, can also be used for stamping, which is useful for killing small animals, putting out small fires, and expressing certain emotions. In the wild, our soles were thick, and we did not need shoes for those purposes. (I once knew a lady from Kenya who in childhood had run 20 miles to & from school every day; she brought such soles with her to college, where they did her no harm.)
Finally, feet can be used for kicking. For that, however, nature has equipped us poorly (by the standard of, say, horses), and I don't suppose there is much of it in cultures that haven't invented shoes. Besides expressing emotion, kicking can be used for breaking things and in various stages of fighting. But in civilization its main use is in propelling small objects for amusement. Kicking is thus contrary to nature in two senses: it is a deviation from the most usual & conspicuous use of our feet, and it requires artificial avoidance of natural consequences. Does that make football a perversion? I leave it to His Holiness to bring that news to Notre Dame.
I recently saw a photograph of the feet of a man whose people spend a lot of their lives climbing trees barefoot. They were not shaped like yours or mine, but they were probably good at what he needed them for. If he came to civilization & were examined by a naive doctor, she probably would look in vain in the literature for the name of his deformity, and would recommend either some elaborate surgery or amputation & prosthesis. She would have a point: As he was, he would have trouble buying shoes, and in his new tribe he would not often wish to climb trees barefoot.
3.3 Sexual organs
The sexual organs are often called reproductive organs, and that is reasonable in that if you or I want to reproduce, the use of those organs is usually the easiest way. It is not reasonable, tho, to say that sex is for reproduction, even in the sense that hearts are for pumping blood or feet are (mostly) for walking. From the top down --- considering first reproduction & then sexual reproduction --- the sexual aspect is an impediment rather than a means. Suppose there were a species that, instead of sexual reproduction, had sexual vision. Half the individuals would have eye sockets with retinas but no lenses; the other half would have no eyes but would have a lens at the end of each little finger. In order for a pair of them to see, a male would have to climb onto a female's back and lock his hands over her face. Wouldn't you wonder how such an awkward arrangement could be selected for, by natural selection or even by intelligent design? And yet, when it comes to reproduction, which is far more fundamental biologically than vision, we take it for granted.
In fact, biologists are not agreed on why sex is so common. It is urged that the mixing of genes is essential to adaptation & speciation; but bacteria manage that without complementary organs and the requirement of one organism from column M & one from column F. Even among animals, there are parthenogenetic lizards and rotifers. (The lizards even go thru the motions of mating. Do they count as lesbians? The alliteration is tempting.) True, the lizards are evolutionary dead ends; but it appears that the rotifers have managed to evolve & speciate without the help of males. The trouble with the rest of us, according to one suggestion, is that in us an obscure but essential biochemical pathway is blocked unless we mate, and the rotifers have found another way around the blockage.
Another idea is that multicellular organisms fall into this bifurcation because of some long-term instability in the very process of their reproduction. Perhaps traits as well as organisms can be parasitic, and sex is a parasitic trait, propagating without actually improving the fitness of the individuals or species it infests. (That might be true, in particular, if it were helpful for speciation.) It does seem that most of the individuals so afflicted are miserable or dead, and most of the species are extinct.
However that may be, it is clear that in judging the use of the sexual organs, an appeal to nature is even less plausible that it is for feet. If there is objection to their being used to express this or that emotion, or for this or that kind of play, then that objection had better depend on details.
Brains are badly understood, and they have a variety of uses, for good or ill. A lot of doctors say they know what constitutes proper fuctioning of brains ("mental health"), but they are bluffing, like the priests before them. Indeed, it may turn out best to say that a brain is not one organ, but a collection of several thousand, forced to live together by their confinement in the same skull and by the needs of cooperation & competition for access to the various sensory & motor nerves, in something like a political process. (Such ideas may be found in The Society of Mind by Marvin Minsky.) If so, then it is likely that each individual is missing some of them thru genetic accident or early deprivation of exercise, so that we are all several dozen kinds of cripple, but manage thru various workarounds. Also, it may well be that an organ's participation in one possible coalition makes it unavailable to others, so that again there have to be workarounds. In such a situation, the notion of normality will not be helpful.