Actually, you do. There already is a "Palestinian state" - it is called Jordan. Is there an inalienable right for the "Palestinians" living on the West Bank to have their own state separate from Jordan? On what basis? And if so, did they have that same right when that land was part of Jordan, or did that right magically arise after the 1967 war?
The population of Jordan is about 50% Palestinian. Most of them were either war refugees from Palestine or their descendants. The idea of a confederation of the West Bank with Jordan was tossed around but it didn't pan out. In line with the Oslo agreement, King Hussein renounced any Jordanian claim to the occupied territories in favor of a separate Palestinian state.