I agree that Biden and Trump are virtually morally equivalent. But there is one argument for avoiding Trump that doesn't apply to Biden or most other Democrats. It is that Trump is very unstable and unpredictable. Take Ukraine. Biden has been careful to limit his support (which I still do not agree with, by the way) to actions that are unlikely to lead to a direct conflict with Russia (though that still doesn't rule out accidental or unintended escalation, which is one of the reasons I'm against it). Trump, on the other hand, would conceivably attack Russia just by being persuaded to do so by someone he likes or admires. Cooler heads in the executive would probably try to talk him out of it, but there is no guarantee they would succeed.

On the other hand, current indications seem to be that Trump won't get the nomination for 2024, or, if he does, he will lose.