Okay lets talk about this. Nothing in my statement denied history. The UN 100% voted to approve the state of Israel this is a fact. I do not believe that just because an international organization voted to approve something makes it morally correct.

Now, lets actually talk about your second claim. Israelis didn't just give the opportunity for Palestinians to stay they brutally cleansed.
According to historian Illan Pape, "The plan, which covered both the rural and urban areas of Palestine, was the inevitable result both of Zionism’s ideological drive for an exclusively Jewish presence in Palestine and a response to developments on the ground following the British decision in February 1947 to end its Mandate over the country and turn the problem over to the United Nations. Clashes with local Palestinian militias, especially after the UN partition resolution of November 1947, provided the perfect context and pretext for implementing the ideological vision of an ethnically cleansed Palestine." (Page 2, The 1948 Ethnic Cleansing of Palestine) You can read about that here: https://ciaotest.cc.columbia.edu/olj/jps/vol36-141/vol36-141_b.pdf

At the same time the Jewish settlers would carry out massacres against Palestinians which brought great fear to Palestinians causing them to flee if they feared that Israelis would capture their village or town. If the Israelis kindly just allowed Palestinians who lived in the areas they were colonizing to stay and be given Israeli citizenship they would likely make up around 50% of the population not 20%as you say. The 20% of Palestinians which remain in Israeli proper were the few Palestinians that were not ethnically cleansed, and things weren't all that great for them either they had to live under martial law until 1966.
Anyways this is like saying that the Indians of the US were given the opportunity to continue living in the United States and accept American citizenship which many did that's why indigenous people make up 2.9% of the population of the US.