I think from a purely strategical point of view, most Americans who actually are much more to the left than the Democratic party will always end up voting Democratic. I would do the same if were American, even though I wholeheartedly agree with your points.
That’s because other candidates get an amount of votes so infinitesimally small, you could be effectively throwing your anti-Republican vote in the bin directly if you voted for any of them. Yes, it’s romantic to vote with the heart but it doesn’t work that way.
No one will ever break out of that loop until the voting system changes. I’ve read the ideal way to structure it is to allow people to rank as many candidates as they wish, and then count all votes and pick the candidate with the most votes… but I guess that ain’t happening anytime soon since it could well be a threat to whoever is in charge at a certain point in time.
I still welcome Americans who have the wish and possibility to come to Europe — Covid-19 and shitty stimulus checks allowing — to move here. As you say, infectious diseases or not, we tend to care about the needs of the many to a much higher extent…