While some of the techniques are illegal, they are not required to partake in the sport. The interest and level of commitment vary from your level to the extreme. Knowing how to achieve the ultimate mileage doesn't necessarily mean it is being sought after.
I think one of the biggest aspects of hypermiling is observing safety. While members may shut off their engine, I think you'll find that they have a very thorough understanding of the function of their automobile, the risks involved, and the amount of skill required. While there are no perfect drivers, I think hypermilers are among the safest on the road.
As far as the A/C failing from disuse, I wouldn't worry too much over the issue. I live in an area where 100+F temperatures are common and have never felt the effects of heat stroke (delusions, light-headedness, etc.), but if you are a sufferer then there are other remedies (evaporative cooling, ice vest, sucking on ice). If the A/C breaks down from disuse, uninstall the thing...it takes up weight.
- LostCause