Judea and Samaria (aka west bank) were part of the land promised to the Jews by the league of nations in the San Remo convention, which is binding by international law and originally also included Jordan. Considering the Arabs have never agreed to the partition plan of 1948 it is well within Israel right to contest this area and the common definition of "occupied territories" is not that clear cut considering no country owned it before 1967.
The settlements themselves don't displace any Arabs from their home, they were built either on Jewish land (Jews lived in Judea and Samaria until 1948) or on a land which didn't have a specific ownership. Usually if an Arab can show that they have ownership for a parcel of land they will get it in court.
In any case, Gaza is not occupied and except from the hostages there are no Jews in Gaza. They could live peacefully side by side near Israel without any "siege" if only they accepted that Israel should have a right to exist.