It’s not problematic to restrict people from selling the thing you designed, made and sell without permission.

If I make an open source car, I don’t want someone else taking my design work, and then selling a cheaper version of my product, I want my consumers to build their own parts.

Then you shouldn’t make an open-source car.

Maybe you should make a source-available car, or a car with select portions of CAD available, or something else that fits your intended business model better than open-source.

Sure, but you're comparing morality to the legal definitions in software licenses.

Different licenses are build around different philosophies, and the common open source definitions allow commercialization as long as the source & modifications you make are freely available to others. Prusa is breaking from that tradition.

then its not open source. That's just shared cad files which mcmaster carr does.

would probably need some hybrid licensing. Like "if you buy a car you have license to print (or order a print) of up to X parts/years"