Israel has been lobbying and campaigning relentlessly for the past few decades to obtain and maintain political support from the West.

The campaign has successfully instilled a few formulas in the public opinion- for example:

1) that Israel has a right to defend itself; (notice how subtly it shifts the issue from that of whether it is defending or attacking, to whether it has a right to defend itself from attacks).

2) that Israel's right to exist needs to be constantly reiterated. (Which implicitly suggests that it's possible the speaker doesn't recognize it- you don't ask somebody who criticizes France to declare it has a right to exist).

3) that the reason Israel is attacked is hatred and anti-Semitism. (And not, of course, that it is violation of international legality and human rights).

4) that there is no meaningful distinction between USA's objectives and Israel's. (While Israel and USA are separate countries and by nature have different objectives).

Some less official but widespread ideas are the negation of Palestinians existence (they are just Arabs) and a "might makes right" principle ("Palestinians have lost and should get over with it").