That letter has apparently been debunked as a hoax, however, King did indeed say “When people criticize Zionism, they mean Jews, and this is anti-semitism” at a Harvard appearance in 1968.
hmmm
that’s why it didn’t occur to me to consider that it was a hoax...
so I found this
http://www.camera.org/index.asp?x_context=8&x_article=369
but the basic point I was trying to get at is that King saw through those who claimed they were anti-zionists and one true sentence makes the point a lot better than a made up essay