re: Why do so many Americans feel we have to always aid israel?

Honest answer to your question is that many Americans are members of protestant denominations who follow the belief of "dispensationalism" which asserts that Jews and Christians will be brought to salvation under different plans/rules, and that Jews are God's Chosen People who will be saved regardless of their belief in Christ, so it follows that anyone who espouses a dispensational doctrine would want to support Israel in everything they do.

Not all Christians hold to this doctrine. Some Christians actually read and study their Bibles and understand that the dispensational doctrine is not taught anywhere in the scriptures, and is little more than a political doctrine claiming to have biblical roots and authority.

On a non-religious basis, Americans have been taught (rightly or wrongly) that most of the nations in the Middle East are strongly anti-American and instigators of terrorism, and that only Israel is a reliable ally in this region.