Israel did not objectively exist at the time. So the Palestinians did not agree to Israel's formation.
If you think about it, UK a foreign country that has no claim to the land, except for the fact that they colonized it, in order to assuage their guilt of a) Not doing anything for Jews in Europe and b) To mask their own anti-semitism during WW2 to the point that they refused to take in Jews who were fleeing, saw this as an "out".
They basically gave someone else's land to a third party, and then spun it off as the right and the moral thing to do.
Israelis even today will not accept a democratic, secular Israel with equal rights for everyone. Israel does not even have inter-religious marriage laws today! They do this deliberately to maintain the Jewishness of their state.
I know you are Jewish (or I think you are), so I don't mean to offend. I am not anti-Jewish, but I am just calling out that the more aggrieved party here are actually the Palestinians.