"It's not anti-semitic to criticise Israel" goes the cry, and it's true. "I'm not against Jews, I'm against Zionists" goes the claim, and most mean it genuinely. And there is indeed a debate about where the dividing line between criticism of Israel and anti-semitism lies.

But here's the problem: both sides are trying to move the line. It's not one-way traffic with a bunch of hard-core pro-Israelis attempting to classify all criticism of Israel as anti-semitic, although heaven knows there are a few of them. At the same time, the hard-core anti-Israelis are pushing in the other direction because it suits their purposes to keep the line as blurred as possible. Not to fix the line - to keep it blurred. A blurred line is more useful, because it permits a maximalist interpretation of where the line might ultimately be.