Sorry, but just because you paid for it, doesn't mean you have a right to excessivly pollute, it may be your rig, it may be your gas (although privatization of such crucial resources is really criminal in and of itself, but it's a hurdle we'll never get over) but it's everyone's environment that your're fucking up and everyone will have to pay for it. The whole "it's my right, I paid for it" is like me saying "I paid for the cola, it's my right to piss all over your yard, and if you don't like shove off".
As for the "It's all I had" excuse, that's b.s. to me, you can get an older civic or vw or anything of that nature for around 500 bucks, and be on the road cheaper than any truck you're driving now, people who drive big trucks do so for two reasons: they need to, or they want to, and the only people who need em are people towing/hauling, plain and simple.
Some people just don't want to face up to the fact that what they're doing IS ultimately selfish, and based on desire rather than utility, and I just love listening to the excuses.