As it turns out though blatant irresponsibility is quite rare (depending on your definition anyway) since people have a strong self interest in not endangering their own lives or wallets. It's similar for homeowners - many states explicitly carve out a requirement that insurance companies cover DIY modifications that are within reason and this generally works out since you have a strong vested interest in not destroying your own house regardless of any insurance policy.
It is. Thousands of people have died because of aftermarket headlights. Harder to assess, but probably much larger, is the number of excess deaths from nitrous oxide etc. emitted by modified cars.
Modified cars can release 1000x more polution, on streets with 800 daily cars that will have an affect.
This isn't complicated FFS.
The difficulty against this in the US is the unfortunate reality that the people coming to these shops to enable their stupid trucks to roll coal are the people who should technically be raiding and shutting down these companies. This can be fixed.
Physically, you can already modify your car to be controlled by a stupid program and that has been possible since at least the 90s. You can do the supposed harm by not being aware of damage to your exhaust system.
The solution to exhaust harms of ICE engines is electric cars, not a reduction in consumer rights.
Maybe you think daytime running lights are stupid and want to disable them for instance.
The risk profile is very different and non-obvious to your average car owner.
It's the difference between trying to repair your leaky dishwasher vs. trying to repair the electrical panel in your basement.
I don't disagree that it's a bit different in certain ways but I feel like that's drifting off topic. It shouldn't be up to manufactures to determine these things unilaterally but rather the legislature. Particularly any justification to the contrary rings hollow in this case because there's a very strong conflict of interest.