That Tweet is a misquote though. He said "he may be responsible for many more deaths" rather than "he may have killed". Very big difference. And he certainly never said that "Trump is literally worse than Hitler". Considering he brings up climate change immediately afterwards it seems he mostly means Trump's persistent war on anything that will slow this down, which will (and already is) causing major problems. A comparison with Mao's incompetence isn't complete inaccurate actually. I do agree it's not helpful, and comparisons to Hitler and Stalin are certainly wildly inappropriate.

But some random guy saying something silly and offensive in one (live?) interview is still not the same as a set of very specific completely baseless allegations in the right-wing conspiracies theories.