From the 'open letter':
"For context, the Hadrianic persecutions of the Jewish people in response to the Bar Kokhba rebellions are some of the defining moments in our history. Jewish culture was profoundly changed because of the systematic destruction of Jewish villages and places of worship, including the torture and execution of the leading rabbis and the desecration of the temple mount. One million people died in the combined casualties of the rebellion, persecutions, and famine resulting from Roman policy in the area. Historians have pointed to this moment as the one where the Jewish people lost its homeland and became a primarily diasporic population."
This is a very one-sided interpretation of historic evidence. The Jewish rebellion was a more complex phenomenon:
Everywhere, where Rome conquered lands, and after the first cruelties had subsided, they included the new areas into the commonwealth of their multicultural empire, worked together with local ruling elites, and made sure that the inhabitants enjoyed the many advantages of the new international context, in which their own culture was left intact and only an 'extra layer' of a more modern civilization was added to existing life, in terms of economic increase, practical progress (roads, postal service, banking system etc.) and a more developed justice system, plus the accessibility of international products including cultural products. As for religion, that was treated as an entirely free choice, as had been practiced in Rome itself. Every conquered people accepted, after a while, Rome's rule as long as they could have the benefits (this changed, of course, over time). The only conquered people who resisted the inclusion within a wider international world which practiced freedom of religion, were the Jews, who differed strongly in their culture and religion from the surrounding peoples which they looked down upon. Their old religious and entirely crazy mutilation ritual of circumcision, however understandable from a people living in the desert, was seen as barbarous by the romans and especially by Hadrian. His attempts to add a Roman layer over an existing culture was then thwarted.
That this sort of religious mutilation still exists, demonstrates some of the irrational and barbaric components of so many religions.
"Rabbinical literature alludes to a Hadrianic persecution that caused fear and apostasy. The probable explanation of this kind of reference is a universal ban on circumcision that Hadrian issued in, it seems, the early 130s. The emperor had an abhorrence of physical mutilation and even went so far as to declare that castration was no less a crime than murder. In the same spirit he denounced and forbade circumcision, which he viewed as mutilation. There is no reason to imagine that Hadrian intended by his measure to punish or provoke the Jews. The uprising came swiftly and understandably."
The personal involvement of Hadrian is, to say the least, questionable:
"Hadrian’s visit to Athens in 131–132 and his residence at Rome until the summer of 134 suggest a reluctance to deal personally with the disturbance in Judaea. He first placed an able general, Sextus Julius Severus, in charge of the problem. In the year after Hadrian’s arrival in the Near East, the revolt was over. Recent discoveries have shown that several measures connected with the close of the revolt and often cited as indications of imperial severity have to be dated at least six years earlier and, very probably, well before that. Hadrian meted out no savage punishments in 135."