Guilt is a strong word. Genocide and fascism are both terrible. The goal should be to minimize both.
If a Democrat gets elected next, will the genocide against the Palestinians stop, probably not. Will the US get more fascist, a little.
If a Republican gets elected next, will the genocide against the Palestinians stop, probably not. Will the US get more fascist, a lot.
It's clear what the better outcome is. If you don't vote towards the goal, then what are you doing? You're taking the moral high ground, to make yourself feel better. Which is fine, but totally unproductive.
We would just be rewarding the fascist party for the mistakes made by the slightly less fascist party. . It's not ganing us any ground.