I agree that Israel should not build on land that is not theirs, but what makes you think that they are doing so. Why do you assume that the land in question belongs to the Palestinians? Consider, e.g., the Jewish Quarter of the Old City of Jerusalem. What makes this Arab land? It was populated almost exclusively by Jews until Jordan invaded the Old City and expelled them. Does that make it Arab land?

In fact, Jews have constituted a majority of the population of Jerusalem for about 150 years, since before Canada was a country.