Are those really from consumer lobbying groups or astroturf? I remember Ralph Nader ran into serious opposition trying to get seatbelts adopted, but that was decades ago.

Astroturf from who? Europe shows that car manufacturers wouldn’t overengineer cars for safety if they didn’t have to. Who else would be responsible for it if not consumer groups?

Companies that make child safety seats certainly benefit from moving the goalposts on safety standards, mandating booster seats, etc.

Specifically why are the standards making the cars heavier than Europe - Europe is not without car safety in the form of EURO NCAP?

I thought fuel efficiency standards were the main driver of weight differences?