But why should American taxpayers be responsible for making the technology affordable for everyone? Why shouldn't Europe or China be expected to shoulder this financial burden?

EDIT: I think people are misunderstanding my response. I fully support local subsidies for solar and renewables. My question is why my tax dollars should go toward making it affordable for everyone, including non-Americans. Either market dynamics will handle that naturally, artificially (i.e., China's manufacturing subsidies), or else it is up to the local government to address the shortfall.