If ethical systems of all shapes and sizes sampled from around the world, all agree that actions are ethically questionable, shouldn't that give the actor even more pause than a small minority of them?

There's no evidence the opposition is driven by antisemitism. The large amount of jewish people who oppose the Israeli genocide of Palestinians should give a clue that judaism isn't the issue here. Russia is trying to do the same thing to Ukraine as Israel is trying to do with Palestine, and receiving equal condemnation worldwide. Only they exclaim "russophobia!" when criticized, rather than "antisemitism!"