The Palestinians neither have a legal nor a moral right to move to and live in the state of Israel. In 1947-48 the Arabs of Mandate Palestine forced an existential war on the Jewish people of Mandate Palestine. The Arabs of Mandate Palestine sought to commit genocide against the Jewish people and prevent the emergence of an Israeli state. Jamal Husseini, a member of the Arab leadership promised that if the UN Partition proposal was accepted, “The blood will flow like rivers in the Middle East.” Leader of the Palestinians Amin Husseini in March of 1948 called for the killing of all Jews in Mandate Palestine, every last one of them.
In the war Arabs used their villages to attack Jewish communities and interdict Jewish traffic. Their intent was to kill and cut off all supplies to Jewish communities. They even cut off Jerusalem's water supply. But the Jews fought and won. Even before the Jewish militias went on the offensive hundreds of thousands of Arabs fled the war. Then as Jewish armies crushed the Arab armies, more Arabs of Mandate Palestine fled to never return.
When the Arabs fled their homes, there was no international law of return applicable to them. The UN asked the parties to make peace and permit refugees who wanted to live in peace with their neighbor to return home or be settled where is and receive compensation. The Arabs voted against the proposal and sought to return to war. So the refugees were left where they were, with no right of return.