What you're saying is a baseless myth. Palestinians are the original inhabitants of the land, and so they where when European colonial migration started in the early XX Century. Defending your land and trying to curtail colonial migration, a migration that has for goal to impoverish you and your community to move them out, can't be called "ethnic cleansing". Get out of here.
There have always been Jews in the land. I can talk of various "colonial" migrations. For instance, how come the language of the land has suddenly changed to Arabic, following an invasion of an Arabic-speaking ruling class?
Third, most of the 700,000 Arabs who left during the 1948 War did so because the Arab leaders told them to so they could get their militaries through and drive the Jewish people out, as this former PLO sniper (whom I met personally) explains in his memoir, and has also been stated by Arab leaders for decades:
Nope. Certainly not most of them (though a non-negligible part). There were various reasons for people to flee.
BTW: No Jew was allowed to live in parts that have become Arab. Not even in the Jewish Quarter of the Old City of Jerusalem, where Jews lived for centuries.
Areas are fenced off in the West Bank to prevent terrorist attacks. Are you aware that if Jews go to Arab sections in the West Bank, like Ramallah, they'd be killed on sight? Why is it OK for over 2 million Arabs to live on one side of the 1949 line, but it's completely unacceptable for any Jews to live on the other side of the 1949 line?