Because America was founded within the Judeo-Christian heritage, the routes of which lie in the Holy Land which is governed by Jews that give freedom of religion to all its citizens and inhabitants, including islamist savages that would destroy Israel and America given the chance.
The Judeo-Christian heritage that we were born from came out of Western Europe which supported centuries of anti-semitism.
Somehow tying our Judeo-Christian heritage to the relatively recent creation of the state of Israel is totally non-sensical.
Just like it took us over a hundred years (and probably more years into the future) to come to grips with our former support of racism and slavery, likewise will it take more time to come to grips with our former support of anti-semitism.
Supporting or not supporting particular policies of the Israeli government is not a sign of anti-semitism except to those race-baiters who profit from focusing more heat than light on these issues.