It's not land theft.  It's a land dispute.  The settlers believe they are exercising their right of return.  They are just taking back their own land that was stolen from them during the Arab conquest of the Middle East in the seventh century.  The settlers believe that the Jews have a deed to the land.  In determining ownership, the law says use the oldest document. There's a Torah that's over a thousand years old.  You don't have to believe in God, but this ancient document lists the names of the owners of the land (the 12 sons of Jacob [aka Israel]) & the boundaries of the land.  In other words, it's a deed to the land naming the children of Israel as the owners.  If you dig in Palestine, you will find ancient synagogues & Jewish ritual baths & Jewish coins.  Settlers see this as further proof that it's their land.
Palestinians say that it's Palestinian land because Palestinians have lived there for centuries.