This is a very entertaining thread. I don't think you'd have seen nearly as many biting comments about Hummers, say, two years ago. I think that says something about the current American mindset.
I don't think it should be against the law to drive a Hummer or any "excessively large" vehicle for that matter. I do think that for the greater good, people should be actively disuaded from buying them, such as via an extra "consumption" tax. Now I think Hummers are pretty damn ugly vehicles and downright impractical for the vast majority of people, but ultimately, it's foolish to try to make laws reflect good taste or interpersonal consideration at this level.
People are free to be dumb.
It's only when their "dumbitude" extracts from the society at large that we need to start to concern ourselves with it (e.g., the above-mentioned consumption tax). Let's be honest, the vast majority of people driving large SUVs would probably be better served with either a minivan or a station wagon. Neither of these is particularly macho, so your average put-upon worker bee who needs to feel a little personal power isn't going to go for one of those. Instead, the SUV creates an aura of power and daring, so the owner can feel a little "special" on his commute to work (and maybe even a little racey if he has one of those NASCAR number stickers on the back). Chances are, the SUV will never go off-road, it will never be used as either a Sport nor Utility Vehicle, but merely as an overgrown, overpriced, resource-hogging transport.
Ask yourself, why do the following exist (functionally, they seem to make no sense): Luxury SUVs, Luxury pickup trucks, 2 wheel drive SUVs, any SUV with oversize wheels and low profile tires, any pickup with air damns, pseudo ground-effects, or other race-like add-ons. Remember, in successful designs form always follows function. In these cases, the function is NOT the obvious "functionality" of a utility vehicle. The TRUE function is something entirely different. Personally, when I see these vehicles I can't help but laugh (in a dark, sardonic way of course).
Finally, always remember that it is not against the law to be self-serving and/or inconsiderate. Some people even consider these to be positive traits. (Can't say that I agree, but there it is...)