If we could harness the heat from nuclear fusion here on Earth, we could use it to generate electricity on-demand without worrying about carbon emissions, nuclear waste, or running out of fuel

I don't want to detract from this exciting milestone. Fusion is an absolute requirement for the complete end of our reliance on fossil fuels and there are no problems significant enough to warrant the end to fusion experiments. However, this statement is definitely not true with tokamak reactors. They typically use deuterium and tritium for fuel, which are limited resources. Fusion reactions are far more difficult with other light elemental isotopes. These reactors also use beryllium as shielding, which is a carcinogen. When the shielding needs to be replaced, it actually is radioactive.