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.

Responding to your edit: A wider version of the same argument might apply. The US has (historically) benefited considerably from global stability and this does seem to help with that because if basically everybody has energy independence and the overheating doesn't get much worse they might chill the fuck out?

Isn't the American complaint that China did exactly that by subsidizing its solar industry and flooding the global market with panels cheaper than Americans could make?

[1] https://www.bbc.com/news/business-20247734 (2012)

China is, it's subsidies have resulted in a glut of cheap solar panel production which the world has benefited from. European counties subsidise their own citizens switch to solar, the US no longer does at the federal level.

Look at it this way: Benefiting everyone is a side effect of benefiting American taxpayers.

Or do you think that US federal investment in solar and battery technology would be bad for the American taxpayer?