If they are so low quality, then let them in and let them fail in the marketplace. I don't think they are so bad. Fleet buses are basically a completely different business btw, that has really nothing to do with private car quality, and besides that, I have a hard time believing BYD buses can be so bad. Probably the SoCal place got an early generation but with the volume they are doing world wide, it's just nonsensical to think it's all garbage.
Manufacturing is tied to national security. Even if those cars are of terrible quality, the Chinese government can subsidize them (they already are) to the point they are valid competitors to normal quality cars. On the surface, this is a win to consumers as this would drive down prices and expand options. But to the US government, this would kill many automakers and factories and reduce national production capacity in time of war.
A very significant factor that allowed the US to completely dominate WW2 was its intact infrastructure and the resulting high manufacturing output. When you churn out ships and tanks in matter of days while your enemy, even with superior technology and quality, takes months to do so, you win. Japan's ships were incredibly well built but they lost the war because they can't replenish fast enough.
