Bottom line is better fuel mileage means one is burning less fuel period. That never seems to be brought up in these discussions. Burning less has a bigger effect in total. Less the refineries have to run, less the pipelines have to push, less the big tankers have to deliver the fuels to the pumping stations, less out of ones pocket.
What you're missing here is, that all this is better, because of the lower environmental impact it has. Less fuel is better, because it results in less harmful emissions. But it results only in less harmful emissions if everything stays the same, including the filter being in place. However, if you're only getting a better mileage because you've removed the filter, then your net emissions will actually increase. And it will increase like up to 20-50-fold in the case of a modern DPF, while your mileage might improve by how much? 5%? So, you've a gain of 5% against the loss of 2000-5000%. The net difference will be still a 1995-4995% increase in harmful emissions.
It all adds up. The electric cars may not pollute but it sure does take a lot of polluting to make the batteries for these cars & the batteries will have to be changed out at least once for the life of the car. Not to mention most countries have to either burn fossil fuels to make their power to supply charging power for them.
Again, all this is about efficiency and net gains. Even if power plants have to burn the same fuel as cars do, they can be run more effectively, and their emissions can also be filtered more effectively, just because of their sheer size and how things scale. 1000 cars with 3.0 liter engines generate far more waste heat and operate far less efficient in total, than does a single combustion chamber with 3000 liters in a power plant, and the latter can also efficiently employ filtering methods with greater efficiency, that are not feasible to be implemented or built into each car separately.
Also, power plants don't have to waste energy on carrying their combustion chambers and filtering equipment with themselves, because you know, they just don't move. But cars have to burn a lot of fuel just for the sake of being able to carry their own engines and filtering equipment with them.
So, even if power plants are burning the very same fuel as do the cars, it still make more sense to burn that in them, than in the cars separately. And of course there are more and more power plants everywhere, that do not actually work by burning fossil fuels.
So it's more about the $ for the gov than the health risks.
If it would be, why would they subsidize technologies that are less harmful to the environment? They are actually losing (carbon) taxes with those, and they are even paying on top of that? They must be stupid. Either that, or your assumption about the evil government being out only for the money and not caring about health/environment impacts is just false.
Carbon tax is just that...tax. Another way to milk the common folk of their hard earned $.
You realize the government can levy tax on anything and everything it wants to, not just on carbon, right? They don't need fossil fuels for that. This is actually the reason why they don't actually cling to combustion engines and are actually subsidizing alternative ways to generate power.
So the EPA pencil pushers can't see the forest through the tree's.
Or maybe you just give too much credit for conspiracy theories, while not being aware of actual facts? See above!
Don't get me wrong, I'm not for everyone to be rolling coal or ignoring the facts that we are slowly polluting our planet. I'm just pointing out the facts the gov doesn't seem to be serious about taking the steps to help clean up the biggest things polluting our planet.
Even if that would be or (let's assume) is true, two wrongs don't make a right, do they? The fact "the government" might not do its best to stop pollution doesn't mean we should go out of our way to cause (or even tolerate others causing) multiple magnitudes more pollution with our vehicles for marginal gains, if any, right?