It seems like there's two potential definitions of "Israel" here that you're confusing: 1. "A Jewish state" 2. "A Jewish state located in the area formerly known as Palestine"

While I agree with you that believing that #1 shouldn't exist is anti-Semitic, I don't see how #2 is necessarily anti-Semitic, especially if the person expressing that view is Palestinian. I believe the Kurds also deserve their own state, but I don't see how that means that, say, the United States is obligated to give them Texas to start one in order to not be anti-Kurdish.

In any case, I, personally, don't believe in any country's "right" to exist. I'm not against any particular country's existence, I just don't think the term "right" applies to it. So am I anti-Semitic for extending that general belief to Israel, too?