What difference does it make if the majority of drivers choose to drive big trucks? You might get slightly better mileage, but it won't impact the demand unless others buy it too.
I'm not worried about impacting demand, but I'd like the opportunity to cut my personal gas expenses in half.
When car makers start making smaller cars that can accomodate bigger people, maybe more truck driving men will switch to cars. Right now, we shop for cars by having my husband sit behind the wheel, and frankly, aside from some full size models, he just doesn't fit comfortably enough to drive more than one hour. Even most of the medium sized SUVs are too small. He's six'6" and either his head hits the roof or his knees hit the dash.