> There's no need to protest when people agree with their government.
Yet there's large protests in countries that aren't allied with the US or Israel, when no such protests were forthcoming in other analogous scenarios. And there were scarce protests in the US against Saudi Arabia's campaign in Yemen despite US alliance.
I do agree that your thesis is a partial explanation, but it is far from a full explanation. There's two other things going on.
Among Western leftists and minority groups, Israel is a symbol. It's perceived as the last vestige of Western/White colonialism. A symbol of someone with white skin punching down on brown skinned people. It harkens back to the reason that your ancestor was forced (either literally or by material circumstance) into the US in the first place, and why you are living today under systemic racism. Defeating this placeholder is therefore an important milestone in restoring their sense of historical justice. Needless to say this is oversimplified given how many Israeli Jews are indigenous to I/P or were ethnically cleansed from the surrounding MENA area and forced into the I/P area, but people do legitimately hold that dichotomous oppressor/oppressed worldview.
Among Muslim countries, this is an ethnoreligious blood feud. Assad killing Muslims doesn't cause the same anger because it's within the same identity group. So it's a classic case of identity divisions leading to disparate anger. I'm massively oversimplifying here, there are many other factors, but it's part of what's behind the energy.