There have always been Jews in Jerusalem ( Since before First Temple , through the sacking of the Second temple and the Macedonian Conquests and the Roman Era and the Dark ages and the Rise of Islam and the Ottomans and the World Wars )I don't believe that the Jews do not have any valid claim to Israel based on some ancient ancestors.
I believe that the Palestinians had some valid claim based on the fact that they were born there.
But, there is no reason why Palestinians and Jews could not coexist peacefully in the same land. The Balfour declaration recognized Israel as a homeland for Jews, but also speified that the rights and property ownership of non-Jews so be respected.
That's the way it SHOULD have been - and any conflicts should have been settled in court.
What I'm against is mass murder and those who support mass murder. The Palestinians have ALWAYS called for the mass murder of all Jews in Israel. They (mostly) evacuated in 1948 to clear the way for the Arab league for the Arab Armies to commit genocide against the Jews.
People have a right to self-defense. Israel's true right to exist is based on their right to self-defense. For as long as the Palestinians keep calling for the murder of all Jews or supporting those who do, then the Israelis have a right to stop the Palestinians from returning to Israel.
And as things stand now, it will be many decades before the Israelis could reasonably trust the Palestinians to have peaceful intentions.