Diesel Question

Why doesn't the government support diesel more?  I know that 20 years ago diesel was associated with loud black smoke belching buses and big rigs.  However this is 2011, we've got clean diesel with 97% less sulfur.....which is good I think.  Diesel cars really aren't that loud anymore either.  Mine is noticeably louder than a regular gas engine, but it's easy to ignore.  The newer diesel cars are even better.  I really don't see the downside to the government supporting diesels more (don't we own a really big car company now?).  I know that diesel is the cheapest gas to make however it is the most expensive consumer gas to buy simply because of taxes.  I don't know for sure but I would guess that the taxes go towards maintaining our nation's highway system.  I wonder how much this tax really hits all of us though.  Think about it, who uses more diesel than anybody.  Big trucks that haul things.  Milk, computers, car parts, paper towels, you name it chances are it got to the store you bought it from in a diesel truck.  Imagine how much the price of all goods in America would drop overnight if the government lifted the taxes on diesel.  Our cars would also average 45 mpg.  Imagine how that would effect our foreign oil dependence.  Because we got such high gas mileage with the cleaner diesel fuel that we have today imagine how that might effect the environment.  Honestly, what is the downside?