If my worldview required me to dismiss 40% of American Jews as being "confused and brainwashed" to explain away why they would possibly be critical of Israel, I hope I would start questioning wether I was the one "confused and brainwashed" instead.

90% of Americans are confused about geography, but I wouldn't dismiss them as people. But I certainly wouldn't trust their judgment when asked to point to Papua New Guinea on a map for example. I think it's pretty easy to see the difference between those two things, but you try to claim they are one and the same.