Why is that even a question? Because some of us consider the suggestion that all selfish or unpleasant behavior should be made a crime to be naive, unpractical and highly dangerous.
It's great if people are nice to each other, and we should certainly encourage that, but the reality is that some people are jerks, and all of us are jerks now and then. Making it illegal to be a jerk isn't going to change that.
For as much as you and others insist that impersonating a person the victim knows is completely different from other kinds of deception, there is a continuum there. Like, how about the guy who pretends to be, I don't know, Ricky Martin, in order to get groupies? Rapist? How about the guy who pretends to be in the band? Rapist? How about the guy who carries around a book of poetry just so he'll seem deep? Rapist? How about the guy who tells his date "Yes, that's my favorite movie too!"? Rapist?*
Deception is a tricky thing to legislate because we all use it (studies have shown that the average person tells a lie, IIRC, about a dozen times a day). Yes, some deceptions are criminal and SHOULD be criminal. I think we all agree on that. But when you're classifying certain cases of something so slippery as one of the most heinous crimes there is, it's only natural that people should ask "So where does it stop?"
___ * For the record, my gut feeling is that something like the Chameleon scenario - with sex - would be rape, the Ricky Martin guy might be guilty of some kind of sexual assault (though I have no idea whether the actual current law would agree), the guy pretending to be in the band would be a jerk, the guy with the poetry would be doing something tacky but within the "rules of the game" (which men and women both play), and the guy with the favorite movie is probably OK.