When is criticism of Israel antisemitic?

There is a myth that any criticism of Israel will be labelled antisemitic. As a longtime reader of Jewish and Israeli news sources, I know that that can't be true. Where does the line between legitimate criticism and antisemitism lie? I like Matthias Kuentzel's take on this in an interview:

Alan Johnson: In the UK the debate has become very confused. The lecturer’s trade union, the UCU, passed a resolution at its national conference that proclaimed ‘criticism of Israel cannot be construed as antisemitic’. When does legitimate criticism of Israel stop and antisemitism begin?

Matthias Küntzel: First of all this UCU resolution is unbelievably ridiculous. It is a historical fact that since the year 1921 there has been an antisemitic anti-Zionism in existence. Alfred Rosenberg wrote his first book against Zionism in that year, and it is completely antisemitic. Second, antisemitism has been a part of Europe for two millennia. And antisemitism is like a chameleon that changes its complexion over time as its environment changes. In such a deeply antisemitic world as Europe, it’s just common sense to look for the ways in which the establishment of a Jewish state would reshape antisemitic thinking. It’s logical to think that it would. In fact, it would be a kind of miracle if this were not the case!

The EU adopted a reasonable definition of antisemitism that includes the phenomenon of antisemitic anti-Zionism. It says that criticism of Israel becomes antisemitic 1) when Israeli policy is equated with Nazi practices or when symbols and images of long-established antisemitism are assigned to Israel; 2) When Israel’s right to existence is denied; 3) When a double standard applies and demands are made of Israel that would never be expected or demanded of another democratic state.

For instance, it is normal for a state to defend itself against rocket attacks from outside. You must give Israel the same right. Otherwise you are dealing with Israel in the same way antisemites deal with Jews. The way the attacks on Sderot are dealt with reminds me of how attacks on European Jews were dealt with in the Middle Ages. At that time also, it was very normal that Jews got punished and beaten, but if the Jew got up the courage to defend himself it was a big scandal. Today, the big headlines only come when Israel tries to defend itself against the rockets. The rockets themselves are treated as, well, normal.