The unfortunate reality is that a not insignificant portion of US voters conflate modern Israel with biblical Israel.
Any stance other than full support of anything Israel does will stick Biden with the Right version version of being racist: an antisemite—and getting that label is enough to get apathetic right leaning voters to go to the polls.
Trump played the Israel card all the time and his base loved him so much for it that they would plug their ears whenever his crimes came to light.
Biden has the unenviable position where if he shows any signs of disapproval of Israel’s actions, he risks another Trump presidency. (Which is absolutely insane considering the whole insurrection thing.)
You’re not wrong, but think of it in terms of Biden tolerating this evil nonsense has the potential to curtail Trump actively encouraging or even instigating more and worse.
Think of it as less kicking the can down the road, as it is kicking the can out of Trump’s hand before he has a chance to pick it up and do something we’ll all regret more.