The issue is that in the realm of international politics, supporting the geopolitical interests of one nation is almost always to the detriment of another - so it is best for nations to support others when interests align. That is the core of Realpolitik. In this instance, unwavering support of Israel has pitted the US against the interests of others in the region and garnered significant ill will. It is worthwhile to question the benefit of the relationship to the US.
Altruism is really a completely different animal, as it does not entail weighing the interests of multiple factions. The choices are much simpler when altruism comes into play. If there were some sort of natural disaster or humanitarian crisis in Israel, I, and I suspect most that take issue with the Israeli stranglehold on US Middle Eastern policy, would have no hesitation about sending as much aid as possible to the scene, as the US always does in such situations. Similarly, if Israel were attacked by her neighbors without cause other than hatred and historical animus as was done in the past, support would surely be forthcoming. However, such situations are not what are being discussed. There is a significant difference between altruism and reflexively vetoing every UN resolution pertaining to Israel, proffering political cover for provocative actions in the region, and sending billions of dollars to the developed nation.
That's where a lot of the support for Israel in the US comes from - misplaced altruism. Most Americans still view Israel through the lense of the David versus Goliath narrative that resulted from the Israeli-Arab wars and the religious overtones it invokes in Christian circles. The geopolitical makeup of the region is much different these days, though. Israel has not faced a threat to its existence in a very long time.
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