micky wrote:

I had figured that if the law required wearing a seat belt,
it would be reasonable to require extenders be available, so one could
folllow the law, and maybe even free, but now I recall that it's only
antilibertarian state laws that require seat belts, Still it seems that
GM does.

If you're talking about the US, the requirement for vehicles to have seat
belts is a federal law. Wearing them is required by all states although they
differ on whether it's primary or secondary enforcement and to the priority
they place on enforcement.

I think my Toyota came with extenders. There is some sort of belt in a
plastic bag under the passenger seat that I never opened and figured out
what it was for. It might be some sort of cargo restraint.