The entire movement for the creation of a homeland for the Jews is known as Zionism, that is what you don't seem to understand. They are one and the same. You can't dislike Zionism, the movement for the creation of a homeland for the Jews, but support their goal. Its nonsensical.
The existence of the Palestinian people. The territory was controlled by the Ottomans but do you really think the people living on the land thought of themselves as Ottomans? Do you think they spoke the Palestinian dialect of Arabic or Ottoman Turkish?
The official reason for the creation of the Mandate of Palestine was to facilitate the eventual self-determination of the people living there. Unfortunately the British horribly mismanaged the mandate and that sowed the seeds of the perpetual conflict to this day, only one among many lies peddled by the European colonialists that have reverberations in the region to this day.
Doesn't matter if there's never been a nation-state there. Nation-states are a relatively recent phenomenon and in the vast majority of cases they are unprecedented but emerged from the cultural milieu of a preexisting people. The Kingdom of Israel was itself not a nation-state so the same applies to Israel. There existed a Palestinian people who were promised a nation-state by the British, therefore there should be a Palestine.
But since you're so preoccupied with the idea of a state there was in fact a quasi-autonomous state in the region under the control of
Zahir al Umar who even attempted a revolt with the support of the Russian Empire and the ruler of Egypt,
Ali Bey al Kabir, thus briefly creating an independent state in historic Palestine. The Zaydani clan from which he hailed still lives in Palestine today.