It's not really all that rational from an economic standpoint alone (unless you count a lot of savings on future health costs, maybe). But neither is buying a hybrid car, if it costs significantly more than a regular car of relatively high efficiency. And people do that all the time, for various reasons. People are a) irrational in their decision-making, and b) underinformed in many ways, and c) not totally driven by economic/monetary concerns alone (for example, some people ride bikes or drive hybrid cars because they believe they're helping the environment, or because it's a status symbol in certain crowds, or because they just plain enjoy it).