Just to begin with, an appetiser as t'were, Tolkien himself owned a car, so where does that place him in relation to his own philosophies? He had a car when he had a family of children so I would suppose that practicality would have been his consideration, as it is is so many things where we must compromise on principle. I'd like to go everywhere on a horse but I dont have the room for one, so I have a car. It doesn't mean that a car is what I'd prefer, simply what I can have.
About the 4x4s (SUVs). I can see exactly why it seems at the least incongruous and at the worst an insult to make use of Tolkien's work to advertise an overly large vehicle, and not least of which, to show it tearing through a forest (no doubt making huge ruts in the ground, running down hikers, scaring the wildlife etc... but that's my own little side rant...

). But I do think the car companies were latching onto the films' popularity. Burger chains
always latch onto the latest films or toy crazes, so it isn't a new phenomenon. Though I do question the logic of the car company concerned in going for this campaign as anyone who has read Tolkien (and that's a mighty sum of people) will likely go "eh?"
Those who have watched the films for 'fun', i.e. those never likely to read the books may well not have got any environmental message at all because it wasn't prominent in the films, so it might be this group the ads were aiming at. From a business perspective, it is clear neither the PR company nor the car company were aiming at book fans, and possibly had little awareness of the message of Tolkien anyway.
There's nothing wrong with analysing it though. We should always analyse the stuff that's shoved at us by the media, as it contains so many messages, not all of which are entirely wholesome. Which gets me onto when messages from Tolkien are appropriated by extremists. Just like advertisers, they also need something which people can latch onto, and that will be why they have a Tolkien quote. It could just as easily be a Shakespeare quote or anything else, just so long as it has a 'brand name' to attach to it, so they can go "hey, it says here...".
But, there is always the chance of someone believing the quote to be the truth, however out of context it might be. This has happened with religious texts. There is the infamous law in the Bible which says it is wrong to eat shellfish; this is often ignored, but the laws in the same passage are often applied vociferously. Can we pick and choose lines of text in this way? Or do we always have to leave them in context? In the same way, can we use the imagery from Tolkien in car adverts? Is it
wrong to do this? I don't know the answer but I like to discuss the questions.