Then, I still wait someone to explain me in the name of which principle US should absolutely defend Israel,
Because we fear what might happen to the 5.5 million Jews that live there if we don't. They do have a handful of neighbors who have repeatedly attacked them and have claimed hundreds of times that they won't be happy until every Jew is gone from the Middle East. We ignore them at the Israelis peril.
We'd do it for any country that is close to us. Can you think of any countries as culturally tied to the US/West as Israel that we wouldn't support if threatened as often as Israel is?