This is a troublesome argument since both sides have reasonable jusification. Yes, UN did approve... but who put UN in charge in the first place? Ever since the exile of Jews due to Romans... Palestines lived in Israel for generations. Europeans just ignored the the natives and created a new nation... like how they foolishly created Yugoslavia.
But the Arabics should have tried to find peaceful solution. Instead, they organized a major attack soon after Israel was created. Israel, having no place to run, naturally countered... and won. In fact, due to Middle Eastern invasion... Israel just got bigger, much of Palestines' disgust. A perfect example of how violence do not solve the problem.... usually.
The fact is that they are trying to point out the enemy's errors and mistakes, which just enrages the opponents and forcing them to attack back. When would they learn that peaceful solution and cooexistence is necessary, if they want to avoid total annihilation?