People don't appreciate that diesel is a very dirty fuel. That is why fuel filters have a so much shorter life than with ones that are filtering gasoline. Even if the filter traps 97.8% of the particle in the diesel that still leaves 240,000 particles going into the engine and out the exhaust with each gallon burned. A lot of new systems were needed to try too minimize the harmful effects of diesel exhaust while allowing their continued use in cars and trucks.
The reality is that diesels are great for the manufacturers with large trucks and SUV's that are low mpg vehicles but also exceedingly profitable ones to make and sell, and still meet the federal CAFE fleet overall mpg figures. The customers pay for the higher cost to purchase and operate and maintain and repair the diesel engines and the manufacturers get to sell more trucks.
It is right that the federal government should be working to minimize air pollution that puts people into the hospitals and that they should be working to maximize fuel economy. After all the federal government spends more than $1 trillion of taxpayers' money (for those of us that pay taxes) to maintain the flow of oil from around the world (with more than 750 active bases). What I pay for fuel at the pumps is peanuts compared to what I pay in taxes to maintain the military war machine that serves the interests of the oil companies and their owners.