And not voting ends up being support for more genocide
Just as I said, your logic works in a situation where either options are reasonable OR, I would add, if there's more than two options and governments are made of coalitions so you can vote for someone that will influence the party with the most vote to move in the direction that you want so they can form the government.
These people would be hypocrites if they didn't vote for him as letting Trump win means more genocide as he'll do nothing about Gaza and leave Ukraine to fend for itself whereas a Democrat can at least be convinced to change his stance.
If Biden wants their votes, he needs to break with the pro-genocide centrist wing of his party and stop supporting genocide. I know this will bitterly disappoint every last centrist Democrat, but you can lecture them that they can't always get everything they want and that they need to vote blue no matter who.
People can not like it all they want, letting Trump take his place by not voting is just virtue signalling and pure idiocy.
"I didn't vote for this guy because he supports Israel!"
"Ok buddy, because of people like you the person now in power supports Israel, stopped support for Ukraine, is attacking women and minority rights... But hey, at least you didn't vote for someone who supports Israel, right?"