You're a reasonable and learned fellow as far as I can tell, and to
some extent you're making me reconsider the "badness" of the analogy when it comes to cars. But I still have several problems with it.
First, most folks using it care comparing all driving to smoking. Quite obviously, one has a great deal of utility and the other does not. Second, even limiting it to "outside" smoking is too broad. At an outdoor gathering where you're stuck in one place (concert, etc.), the same problems occur with prolonged exposure--eye, nose and throat irritation, stinking up clothes, skin and hair, health risks, etc. Unless you're in a traffic jam with your windows down, this isn't happening with car exhaust.
Third, the smell and the health risks don't appear to be as bad with car exhaust. I work in downtown Chicago--lots of cars all the time, of course--and really, about the only time I smell exhaust is when I'm standing too close to the road after I get off a bus and it leaves. Admittedly, I'm far less informed on the health risks, but I'm not aware of any studies proving that people in busy cities are dying or getting sick from exposure to exhaust. (Note: I'm not denying that it's bad for you on some level.) On the other hand, I encounter the smell if cigarettes around building entrances and when I get stuck in an elevator with someone coming off their smoke break. (That's a real treat.)
Fourth, and this is really the biggest thing for me: Smokers and drivers aren't separate groups in the least. Heck, given cigarettes' cardiovascular effects, smokers might drive a little more often than nonsmokers. The effects of their smoking are layered
on top of what they're doing with their driving. Person A drives to the movie theater and sees a movie. Person B drives to the movie theater AND smokes while waiting in line if the box office is out front AND leaves the butt in front of the theater and sees a movie. (Not that all smokers do this, but it happens with regularity in my experience.)
Here again, smokers probably fart, play bad techno and are loud and obnoxious just as often as nonsmokers. Actually, given that loud, obnoxious people are often drunk and given the obvious link between drinking and smoking...

Sorry to repeat myself, as you've surely gotten my point, but there really is no "other people". Smokers are part of those other groups, too.
I don't mean to sound flip about this or cop out from a more philosophical discussion of these issues. But I had to make the above point and my post is getting absurdly long (and my time short tonight). I have seriously tried to come up with an activity comparable to smoking that is engaged in by a particular group that leaves others physically irritated and smelly long after the fact, exposes others to health risks and yet is still legal to do in public. I have yet to think of one.