a lot of it comes down to priorities, rather than disagreements.
if my primary concern is foreign policy, i may see trump as the lesser evil, because i'm concerned about biden's bellicose, pro-war rhetoric and history of supporting major armed conflicts. i might even win that debate with a jello, who i know is not kind to liberal interventionists. but, he might counter that climate change is more important, and biden offers a marginal improvement; a point i may concede in theory, even if i think it's unlikely to actually manifest itself in reality.
so, we're not really disagreeing on policy, or even on who is worse in specific contexts.
we're disagreeing on the ballot question, and that's the difference between my own suggestion to vote green in protest against biden, and his to join the choir and hold his nose to push out trump.
like i say: if somebody wants to have that debate, send me an email and we'll have it.