perfectly safe and clean modern vehicles from other advanced nations
The UK, for instance, allows pretty much anything with wheels to be registered (e.g. the Peel). Euro NCAP is merely advisory, you can still sell/buy a death trap. Pollution as well. Want an early 90s Figaro or S-Cargo or a late 00s Hijet? Those were sold without cats or fuel injection. Want something cheap and Euro? Cool. The cheap shit is often cheap because it pollute so much it can't be driven in city centers.
A lot of the bellyaching is over cars that the manufacturers couldn't justify fixing up to meet American standards.
Obviously there are many confounding factors, but the point is if the USA really cared, it'd federally mandate more effective measures like safety inspections and emissions testing. The import restrictions are protectionism.
Of course we shouldn't be allowing people to import some pollution-spewing deathtrap that doesn't have seatbelts--the FMVSS regulations do exist for a reason--but I think we should be taking a more critical look at our regulations, especially as compared to other places at the same socioeconomic level.