On the contrary, thinking like this is what spurs real innovation.

Look how many comments in this thread are about trivial changes like cutting the size of cars by half, or doubling fuel mileage, or cutting speeds in half. Likewise, think how many people assume you can make an appreciable change in global warming by recycling a bit more, driving a bit less, or buying the right brand of milk. What these all have in common is that they seem much easier to implement and, crucially, they make you feel like you're doing something.

In fact, we need major innovations. The point of my back-of-the-envelope argument isn't to assume that new solutions look like old ones. (I mean, I take it as obvious that, e.g., if we have ways to wireless beam energy to moving cars then this is an awesome solution and brilliantly defeats my argument.) The point of the argument is that you can't make minor changes; they have to be ambitious.