[coldtea]

>From a mpg(society) perspective, some urban commuter might do far better in a Prius than in, say, a Suburban. This might be the result of advertising and also a net gain for society.

Yes, but advertising is neutral to that. It will advertise a low-mpg smog-emitting monster just as well as a Prius.

And it will prioritise advertising cars (which make them more money) over public transit or bicycles and so on.