Because it contradicts what Israeli, Palestinian, and non-aligned historians have said. The Lavon Affair was a real thing but your pretence that all Arab persecution was false flag is conspiracy.
Sad that you only see the world in extremes. Most rational people would see the flaws with Israel while still seeing the flaws in the Arab world and Palestinian leadership. For example, you seem as blind to Arab terrorism against Jews in Mandate Palestine and are willing to pretend that one event shows that it all was 'false flag'.
p.s. Chomsky is a linguist and a political activist, not a historian. The fact that he is of Jewish descent only matters to people who see the world in racist absolutes.
I don't see the world in extremes. But it is you who denies that the Zionists never did anything wrong, which puts you in the extremes camp. Rokach's book is directly based on the diaries of Moshe Sharett, the SECOND PRIME-MINISTER OF ISRAEL. It is not rumor nor innuendo but the real thing. Her book was published in English when Sharett's diaries were in Hebrew only by court order, and not talked about in Israel because they were embarrassing to the cause, and contradicted the narrative that Zionists were so much better than anybody else.
In reality, it's been a continuous land grab since 1947, and land grabs always have nasty undertones.
The Lavon Affair was just the tip of the iceberg. This was confirmed to me by a few Jewish colleagues, namely Sephardim who came from Arab lands.
If you care to watch the interview with Gabor Mate, an ex-Zionist, he is of the opinion that the Arabs had every right to resist the invasion of European Jews who wanted to take over their land and kick them out. You have a black and white view of history; in reality it is more like many shades of gray.
Chomsky doesn't have to be a historian in order to have credibility. He has the courage of saying it like it is. He is world renowned for his commentary on geopolitics, and only those who push the narrative will try to undermine him with cheap inferences of 'only' being a linguistics professor.