A modded car is not only one that has had work done to the engine. Many people put on larger and wider wheels, lowered suspension and a window tint, all of which have obvious benefits that do not detract from the safety of the vehicle, but actually improve it. Manufacturers themselves offer the same features as options on some of their cars, too. If you want to use the minority of poorly modded cars as your benchmark, then you're no better than the cops (who themselves drive around in modified cars).
You do know that widening your tyres and/or track directly affects the turning of your vehicle and increases the loads on your suspension?
Purchase a new car and do a non-factory ''upgrade'', then take it back for a service. See how they react. A mate of mine had to remove his 70k worth of shocks, mags and tyres (not cheap, no name stuff either) from his Beemer as it was still under warranty. They argued that the vehicle was not designed to run with the sizes he installed and thus his warranty would be voided if something related to them failed, ie a suspension component.
Mods done by the local hot shop do not equate to factory-fitted options, which have likely passed necessary tests and will not affect the safety and handling of the vehicle.
Then you're missing the point, which was that in FIA-sanctioned motorsport, manufacturers themselves use aftermarket performance parts, and that the parts themselves ensure improvements to the standard vehicle when used in real-world scenarios. Audi, for example, use Bilstein shock absorbers in their Le Mans vehicles. If the manufacturer sees fit to trust the components from these aftermarket manufacturers, why should the public be disallowed from doing so?
Thing is, I doubt Audi Sport purchases a set of Bilstein shocks off the shelf. Those are more than likely designed and manufactured to the specs of their LMPs cars and that is all carried out by qualified engineers. Obviously Bilstein don't make nonsense off the shelf products, but, a quality, reputable product does not mean quality workmanship nor does it guarantee that the correct components in relation to the vehicle were used.
My argument is this; Audi Sport employs qualified people to carry out engineering work and has things specially made for their racing cars. There is no guarantee that a mod shop is run by qualified guys. They could be guys that have ''taught themselves'' and they are using universal products for a wide range of vehicles with differing baseline performance capabilities.
And let us not kid ourselves, the majority of mods are to do with looks and speed, not safety.