The Balfour Declaration was widely rejected and opposed by the Arab Palestinians, as well as the broader Arab world. This is because the declaration promised the establishment of a "national home for the Jewish people" in Palestine without consulting or taking into account the rights and aspirations of the indigenous Arab population.
For the Arab Palestinians, the Balfour Declaration represented a violation of their national rights and a threat to their presence in Palestine. They saw it as a form of colonialism, in which a foreign power was promising to establish a Jewish homeland on land that was already inhabited by a large Arab population.
The Arab Palestinians also saw the Balfour Declaration as a betrayal of the promises made by the British government and other Allied powers during World War I, in which they had promised Arab leaders that they would support Arab independence in exchange for their support against the Ottoman Empire.
The Balfour Declaration also represented a violation of the principle of self-determination, which was gaining support in the international community at the time, and which recognized the right of peoples to govern themselves.
In summary, the Balfour Declaration was deeply rejected and opposed by the Arab Palestinians and the Arab world, because it promised the establishment of a Jewish homeland in Palestine without consulting or taking into account the rights and aspirations of the indigenous Arab population, and it was seen as a form of colonialism and a violation of the principle of self-determination.