It's not the only capitalistic way to do it. You could have private companies developing the technology but a government testing program to demonstrate some level of safety.

That is what they do with impact crash testing. Private companies design cars, and then the government crashes some to see how they do in certain scenarios.

But, the US government isn't taking this route right now, probably because they believe that SDCs have the promise of reducing traffic fatalities over the long term, so they don't want regulation to delay the process. But that's a policy decision based on calculated risk, not a necessity of a capitalist system.