Why do we treat unwanted touching of some parts of the body different from unwanted touching of other parts of the body? (Obviously, I'm referring here to unwanted touching, not beating someone, holding someone down, or otherwise injuring them.) And why do we treat being nude or having sex in front of unconsenting others as a crime?

It seems to me that the two may be related. In an earlier post, I suggested that one similarity may be that both may involve "a connection with sexual arousal — either the possibility that you might be involuntarily sexually aroused, or the likelihood that the other person is deriving some sort of sexual arousal from touching you." If someone rubs a man's penis in a public place, for instance, the man may feel involuntary sexual arousal (though even if the touching is arousing, it might be unpleasant, precisely because it's done without the man's permission). Likewise, if two people are having sex in a public place, passersby may also feel such involuntary arousal (though I stress again that the arousal may be disgusting rather than on balance pleasant, precisely because it's unexpected and unconsented to). Such messing around with others' hormonal systems, it seems to me, is troubling in a way that an unwanted pat on the back or the ounesthetic but nonsexual display of, say, an unsightly belly is not.

On reflection, though, I think I probably overstated the importance of this factor as to unwanted touching, and understated the importance of the other factor that I mentioned: "the likelihood that the other person is deriving some sort of sexual arousal from touching you." Even if you feel entirely unaroused (neither pleasantly aroused nor, more likely, unpleasantly aroused) by someone caressing your private parts in public, you may feel quite upset by the likelihood — not certainty, but likelihood — that this other person is deriving some arousal from the action, and from your involuntary involvement in the action.

That too helps explain why we treat unwanted pats on the back differently from unwanted pats on the breast or on the genitals. (To shift for a moment to a much more intrusive but necessary touching, I take it that many of us would be quite upset if we learned that our gynecologist, urologist, or proctologist, who has to touch our private parts, is actually being aroused by the touching, or, worse still, is engaging in the touching because he wants to be aroused by it. Here, we probably must acknowledge some risk of the arousal — but I suspect most of us try to put it out of our minds, and most certainly would not enjoy learning that the risk in this instance is reality.)

And it might explain why we're quite upset by at least some forms of public nudity and especially public sex. If I see someone masturbating in a public place, I'll probably assume that he's doing precisely because he gets his jollies from being seen by unexpecting passersby (maybe not passersby quite like me, but at least some kinds of passersby). Perhaps it is this sense that the person is likely to be deriving some sexual arousal from others' involvement in his act, even if the involvement is simply observing, that makes it an offense against those others.

I'm not sure how apt this explanation ultimately is for all cases of public sex or public nudity, especially ones where it doesn't seem terribly likely that the people engaged in the act really are doing it for the sake of sexual exhibitionism. But the risk that sexual exhibitionism is part of the motive, and thus that the viewers are in a sense being involuntarily used (though without physical touching) for the actor's sexual gratification, seems to be present in at least many instances of public sex and nudity, to the point that a prophylactic rule against such conduct (except when only consenting viewers are likely to be present) seems sensible.

As I said in the earlier post, I'm not positive about this, but it seems to me that there's something interesting and possibly important in play here: Some conduct that sexually arouses a person through the unwanted participation — even visual — of another may be improper, even if similar conduct in which sexual arousal is absent is generally fine.