The Palestinians left in the expectation that it would be better to return alive after the Arab armies conquered than to die at the hands of Irgun and Lehi terrorists like those at Deir Yassin who had foolishly believed that if they were peaceful, they could receive peace in return. It wasn't until after Deir Yassin that the Arab governments recommend that Arabs leave before they could be killed by Zionist thugs. If they hadn't left, I fully expect that thousands more would have been massacred at the hands of those criminals.
Not all of them left, why didn't it happen over and over again anyway?
This is one of the stupidest anti-zionist arguments one can ever hear. So you want the Jews who were nearly exterminated by the Germans to take over a section of Germany....in 1946? What kind of morons would the Jews be if they had accepted it and as Ray points out, it was certainly never an option anyway. This is in the same level of stupid as calling Somalia a libertarian paradise or the claim that a black market is a free market because the govt isn't involved.