>>1
The two main benifits are fairly simple, as I see it.
First, one can retrofit a car to run biodiesel, while switching to something else would basicly require a new car to use. The thing is that the more cost that's associated with switching to a new fuel, the harder it's going to be to get the average middle/lower class people to buy into that fuel. Most cars on the road are *used* cars, and in fact the vast majority of people buy used cars rather than new ones. For the rich folks out there, maybe other fuels look pretty good, but remember if people can't afford to make the switch, they won't.
Secondly, Biodiesel is renewable. That's probably reasonably true for other types of alternate fuels. But if your main goal is to get people off the jihadi oil tit, being able to grow an automotive fuel is important. People in the USA just don't seem to go for public transport the way Europe does, so you need to fuel all of the trucks diven on US roads. I'd rather the money go to corn farmers in Kansas, Missouri or Illinois rather than the middle east.