He's an Israeli socialist who used to write for Haaretz and served as a spokesman for Mapam, the Israeli Socialist Party, to the Knesset. He's definitely no Likudnik, but I wouldn't say he is an anti semite because he is also a Russian Jew who served in the IDF after performing Aliyah and has translated rabbinical works.
As far as I can tell the accusations mainly are because he supports a 1 state solution and full rights for all. He does deny certain aspects of the holocaust, but not that it happened, he actually lost family to it.
As far as I am concerned he is a Jew and that is good enough for me. He can have any opinion he wants about Palestinians.