Yeah.
[Suggestion (NOT directed to MCummings):
Please (Aren't I polite?)do not "skim" this post and then start name-calling at high volume. It is written for thoughtful readers. ]
Let's remember the thread title -- "Smoke & your 6. 7L".
We'll get back to it.
But first a bit about those elements associated with fuel consumption of which I am supposedly completely "ignorant": There is a nursery rhyme called "The House that Jack Built", I believe, which breaks down the building of Jack's house into components. In the same way, we can start wherever we choose, and begin compiling environmental costs associated with fuel production and delivery to the truck stop, ... thence to our tanks, ... thence to our engine.
Iron ore is dug/smelted to make steel for a chair frame, a sheep is raised and sheared for some wool (or some oil is pumped from underground for synthetic fabric), a chair factory is built(easier said than done), and its product is transported to an office in which a mechanical engineer (with a secondary degree in metallurgy) works. After driving to work in his polluting vehicle, with its own production history, he then sits on the fabric covered seat of the chair, leans over a drawing-board (or computer) with ITS own production history, and begins to design the drill bit to be used on the next-generation of oil-well drilling rigs.
... and so it begins.
We could continue this detailed envisioning ad-nauseam, noting drilling sludge and run-off at the well-site, oil spills, tanker-truck emissions during transport, etc. (don't forget the particles of rubber tires ground off on the highway), until we end up with a pump attendant(in some states) who smokes cigarettes on his breaks,... adding some more pollution to his lungs (We'll help pay his hospital costs) as well as the atmosphere. The last item is a "fuel" cost because the pump-jockey only started smoking because his job is so da*ned boring,... and because he is not-allowed to smoke near the pumps,... thus a forbidden-fruit appeal.
All of this to give us fuel to feed our "favorite truck".
All contributing to the enviro-costs of fuel usage
Yes, but, ... beside-the-point of the thread.
Beside the point because: That oil WILL be pumped/delivered, until it is gone, no matter how much-or-little ANY one of us uses, ... because ALL of us will use ALL of it, ... every last drop.
All-of-us includes, for example, the Chinese, who are just starting to roll, so to speak, and as the whole world "progresses" to anything like the U. S. level of consumption, the inescapable costs of fuel production/delivery (both enviro and other costs) WILL be paid by everyone.
So, ... since some or most these costs are unavoidable (or at least unlikely to BE avoided), we might look at some that are not unavoidable.
We'll look at our end of the story, ... the "use" end.
Which leads us back to the thread title - "Smoke & Your 6. 7L".
And the fact that if our individual use, regardless of our individual mpg, does not add ADDITIONAL harmful emissions to the environment,... then the environment has been "protected" (EPA, anyone?) to some degree.
That degree depends upon how many of us "ALL" are using the fuel in vehicles which do-or-do-not "smoke"(emit harmful combustion products).
If the goals include a cleaner environment (Everyone who is for a DIRTIER environment, raise your hand.

), ... It would be nice if we all could/would drive the smoke-free vehicles. But to expect 3rd-World countries(for instance, as another poster has suggested) to leap-frog over all our past excesses, to a position of great regulated-responsibility, while they are still struggling to emulate our pre-eminent example of wasteful consumption, ... is unrealistic.
WE have set the world standard bad-example,... and so it is appropriate that WE should set the good-example standard needed for a better future.
A last ironic observation about mpg:
Poor mileage is best(HUH?), from an environmental standpoint, IF the fuel is used in smoke-free vehicles, for the following reason:
ALL the planet's fuel WILL be used. When all is said and done, if a greater percentage of it has been burned in non-polluting "burners", then there will be a smaller amount of "total" polluting done as a result. (Get out there and DRIVE those 6. 7's!

)
So, as I said before, ... effective emissions control, which may be inconvenient (costly) for the operator, ... is nevertheless "good" for the environment, ... mpg is a separate issue.
[Thanks to those who have PM'd support. Controversial topics can make for interesting discussion, ... but with such wide readership some ruffled feathers are a "given". ]