With regards to your 1st comment, I never said that people should have to justify their choice of car, all I said was that if they choose to buy what can very reasonably be classed as a luxury car, then they should expect to pay more to tax it. What, may I ask, is wrong with that?
With regards to your 2nd comment, yes: the vast majority of cars will indeed be scrapped or banger raced when they become old and worthless. And yes, a certain amount of 4x4s will die on farms rather than going to a scrapyard when they fail their mot. However, this has no relevance to road tax.
With regards to your 3rd comment, please don't take this the wrong way, but you come across as someone who is rather comfortably well off financially, so you can't seem to grasp the fact that some people quite simply cannot afford a "clean" car, be that 1 bought outright or a monthly repayment for 1. A lot of people can only afford to run an old banger and these people shouldn't have to pay an arguably excessive amount of tax, purely because their car is of an older design. As much as anything, you argue that people shouldn't have to justify why they drive a huge car, so therefore, why should people who struggle financially have to justify why they drive an old "unclean" car?