Let's say, for argument's sake, everything you say is correct. So what do we do about it now?
If you look at the beginning of every national state, you'll find wars, invasions, conquests and displacement. A perfect example is the United States. Did Europeans have a right to invade America and steal an entire continent away from its native inhabitants, pushing them off their land, herding them into reservations, waging wars and committing massacres? What's done is done. You can't change history.
Israel has been in existence for over six decades and is home to nearly seven million Jews. Less than 50,000 Palestinians remain who ever set foot inside of israel. They should accept it, get over it, stop whining and make a real peace with Israel.