I have long been of the belief that U.S. foreign policy toward Israel leans toward being obsequious, tolerant of abusive practices, and hypocritical. The same goes for U.S. foreign policy toward Saudi Arabia.
I had a friend who was very big on Bible prophecy, and he literally believed that it was God's will that the U.S. support Israel no matter what. I didn't really understand (nor much remember at this point) his reasoning, but he was very firm on this point. I've heard televangelists say similar things, suggesting that America and Israel have some special role to play in Bible prophecy. I've never even seen the words "United States of America" anywhere in the Bible, so I don't know how they come up with it.
But apart from that, historically, a lot of different factions have found reason to want to fight over that particular piece of territory, regarded by many as the Holy Land.
Other than the religious considerations, we've had a longstanding alliance with Israel. For a time, it was perceived that some of Israel's enemies were being backed by the Soviets, so U.S. support of Israel made some degree of sense on that basis alone. It's also strategically located. There's also the idea that, since we've been allies with Israel for so long, it would be seen as a betrayal if we turned our backs on them now. My high school government teacher (early 80s) suggested our relationship with Israel is like a marriage - for better or worse.
As for our policies regarding Saudi Arabia, I think the main explanation is oil - and keeping other potential rivals away from the Persian Gulf. It's also why we installed and supported the Shah of Iran. Actually, that kind of policy was also commonly practiced in Latin America and the so-called "Banana Republics." We'd install murderous dictators in order to protect the free world from tyranny. We've also seen such practices in Africa and Asia.
I never thought there was any valid justification for any of this, and most of the Cold War propaganda has pretty much fossilized at this point - yet our leaders and policymakers can't think of anything better to do. Some of the more cynical among us might look at US foreign policy from a national interests point of view, an apologia from a quasi-imperialist standpoint, since the US has become so wealthy and powerful as a result. "It's all about economics," as the line goes. Some of it comes across as slightly conspiratorial, so I won't necessarily endorse it, but I would observe that, even if it was true, US national interests appear to have suffered immensely as a result of wasted resources, bloated military budgets, bureaucratic mismanagement, and geopolitical short-sightedness.