I think you are absolutely correct, particularly in a real politik sense.  US policy likely hurts US interests.  But I think most Americans believe that the Israeli's deserve, what they view, as a "fair shake".  There is a strong Christian population, and a Jewish one.  The "Exodus" movie and book, most of us were raised on.  So they just look like a scrappy group, that has had a lot of tough breaks over a couple of millenia, and Americans believe need to have a little land to live in peace.  I believe that polls over time bear this out, example.

I'm not arguing the case btw, as I know there is a very clear Palestinean argument,,,but I think this is the reason, and in reality it hurts US national interest--but viewed as just the right thing to do.