This is clearly tongue in cheek I wonder if they asked him to write something with high brow humour. The last paragraph gives it away, but in order to see why i

This is clearly tongue in cheek I wonder if they asked him to write something with high brow humour. The last paragraph gives it away, but in order to see why it's a giveaway you need to be able to understand why, which I'm guessing the people who asked him did not. In short for those who missed it, proud and justified superiority is a key reason why we still have economic classes which cause disparity and wars (particularly ethnic cleansing and WW2 which would have been in Einstein's mind when this letter was penned as it was just starting). Or maybe he was just humourously illustrating his predisposition to it too (i.e. call people stupid, illustrate you make the same mistakes).