I have taken Dennis Ross's account of the Clinton/Arafat talks as being more or less true. It differs from Lerners in important ways. If I believed Lerner's account, I too would be upset. I too believe in tikkun, if only because political action in this world would be impossible without believing in it. Or perhaps it would be more accurate to say, I have faith in tikkun, because history doesn't give us much evidence of its plausibility.
I also would have see his sources for the statement: "Hundreds of thousands of Palestinians fled their homes in 1948, and recent research by Israeli historians has shown most fled not because they were responding to the appeal of Arab leaders but because they feared acts of violence by right-wing Israeli terrorists or were forced from their homes by the Israeli army." I have heard this before, but have never seen any evidence of it whatsoever. I believe the contrary partly because I spent time in Israel in the late 60s (after the '67 war), met some of the Army vets and people who had lived there since before independence, and grew to like and trust them. And I heard a lot of the Arab rhetoric about Israel. It made sense to me that they--the Arabs--would be outraged at the two state solution that the UN adopted. And it made sense to me that they would not accept it. Also, I have seen pro-Arab (not pro-Israeli) documentaries that show people who left their homes and regret it--and they say that they left because the Arab countries promised them it would be only for a few weeks or months, until they drove infidels out. They were saying these things. Many people, including even Jewish people, believed it. They were not saying that they left because the Jews drove them out.
To put it bluntly, Lerner would have to produce some credible evidence to back up this contention. On the face of it, it seems wrong to me.