I have a friend who is a music mixer/engineer. He hates it when people muck about with the sound.
Engineers/mixers/produces and artist spend hours getting the music to sound just right. Then so person turns the bass up and ruins it all just to grab attention as he approaches the traffic lights
What makes your friend think that a car set up is anywhere near similar to a studio set up? In a studio you haven't got all manner of bass frequencies coming up through the chassis that you have to overcome to get the 'correct' sound lol
Not only that, I'm quite sure that a studio set up runs a number of high-quality, large-diameter drivers, with similarly high quality components for the top end, all housed in specially designed sealed or ported enclosures - not 6 inch speakers slapped into an infinite baffle door, struggling to cope with the entire frequence range!
I take your point about chavs turning up standard speakers and ruining the sound with distortion in some cases - this is why subs are a benefit, because they remove the bass from a small-diameter speaker and enable it to deal better with the mid and high ranges.
Same goes to car manufactures. Nearly all non budget cars. especially rep mobiles have had a lot of time and effort going into the stereo set up.
I don't doubt this. I would point out however that a lot of cars that have subs put in them don't fall into the "non budget cars" category, and even those that didn't when they were made won't be as good as new set ups as speaker and soundproofing technology moves on!
Anyway, I'm in an argumentative mood, and I don't think either of us is going to change to the other's point of view... lol