I think some people just have a default setting of hating BMWs and hating anyone who drives one, as if it says something about them as a person.
It appears to be quite a common and bizarrely intransigent position. If asked to define exactly why, I doubt they'd be able to come up with any kind of logical justification.
Wanting to drive 'luxury' or high quality as I prefer to call it, is no different to wanting eat, drink or wear it, or sleep in it or sit on it. Some people just aren't very discerning and they profess to not being able to tell the difference. But then perhaps they have never experienced the difference enough to be able to make a serious comparison. I think this is probably more true of cars than of anything else. If they can't afford to experience the difference then that's fine. But to justify that by telling other people that they are somehow stupid or shallow for appreciating quality really gets on my tits. It doesn't matter whether you are talking about the difference between an entry level 1.1 Ford Fiesta with no frills, or a top of the range S-Max with a superb engine, or an BMW v. an Aston Martin. It's just a simple case of understanding that you get what you pay for.
Clothes for example; it's about the way they are cut; the way they hang, the quality of the stitching on the seams and the hems. Do I waft around in beautiful haute couture all day? No. Because I'm too fat so I think I don't deserve it or do it justice, and I don't go to enough places where it would be appreciated or seen. But if I lost three stone and went out more, and I could afford it - you betcha I would be head to toe in lovely designer gear. I could practically orgasm just thinking about it.
But I can drive nice cars and wear a nice watch and cook with great quality pans and knives and sleep on great quality sheets because I don't need to be a size 8 to do that. 
Take cheap washing machines for example. It'd easy to think that washing machines all do the same thing - why pay 700 quid for one when you can pay 250? Well it will be quieter, it will use less water, it will have a greater range of programmes, it will not rip/snag your clothes, it will have a higher spin speed to remove more water so clothes cost less to dry, it probably last you 10 years instead of 3, the build and the components will be better quality, it will be more energy efficient and cost less to run etc., etc.
Some things just look far more beautiful for being expensive, but other things actually do the job better and last longer. A decent car does both.