To be clear, was attributing the simplism to people like the one you linked. Also, I'm not comfortable attributing improbability to the Zionist project: In retrospect it appears, of course, absolutely necessary.
As for the Boer question, "indigeneity" would be one potential contribution to a natural right argument. One can imagine a natural right argument without it, as in the claim that the land belongs to the one who works it or the idea of possession being 9/10ths of the law, and so on, but one can imagine the same natural right argument being strengthened with it: "He works it all day long, just like his forefathers, and has always been accepted by everyone to be the true owner of the land" and so on.
In the case of the Israeli Jews, there is the claim, of course, that the Jews have maintained a continuous presence in and around the Holy Land for thousands of years. There is the related claim that the Jews have always maintained an "identification" with the land, a recognized identification, regardless of the physical location of particular Jews at any given time or over any given period of time. The significance attributed to such claims is demonstrated by the efforts of Palestinian Arab theorists to dispute them on their own terms, or to claim that, whatever can be said about the Jews of Palestine, the Diasporetic Jews who immigrated had no authentic genetic or other material connection to them. With the Boers there was no such controversy. They wore their (relative) alienness to the land on their skins.
Previously to the 1920s, the very low estimation of a Palestinian national project - as non-existent - was captured in the slogan "a land without a people for a people without a land," which apparently pre-dates Zionism as a formalized movement. To the extent a latent Palestinian Arab national potential was recognized, Zionists tried to pre-empt it financially, obtaining deeds to the land through the then sovereign power, the Ottoman Empire.
Though I agree the question eventually goes to the very possibility of "human choice, free will, and morality" - or in short of meaningful justice - the nationalist or statist premise is that justice is conceivable only after, not before, the foundation of the state. Prior to the state there would be only the state of nature. During the period in which Zionism was consolidated, colonialism wasn't generally taken to be an evil, and the Wilsonian Era notion of a right of ethnic self-determination also didn't exist or was still being formulated (as a kind of corollary of nationalism). The inhabitants of a land that could be colonized were considered to be subsisting at a lower level of civilization, or prior to civilization. One might be expected or asked to treat them humanely, but not to recognize a legal right of possession on their behalf. Remember, at the time Americans were still busily completing the settlement of North America, and the European powers were competing with each other for control over vast expanses of the present day "developing world."
By the time of the 1947 partition plan, the colonial era was over, but not the national era. The latter was entering its often brutal consolidation phase, especially in formerly colonized areas, including Palestine. The Zionist project was and remains a project with qualities of both colonialism and nationalism - in some ways like that of the Boers, but with important differences as well, including a significantly more credible claim of naturally rightful ownership based on indigeneity.
The map also illustrates the extent to which the project had already advanced, and put a binary choice before the world. The world pretended that it could divide the baby in half, but neither side believed in the justice of the decision, and both rejected it, even though the Zionists, typically and indicatively for the practical superiority of their claim, were better able to negotiate the legal and historical, as well as material and military, complexities. They understood that they could formally accept the decision, then use the other side's formal rejection of it to advantage in sorting out the resultant mess.
Rightly or wrongly, or beyond good and evil, or perhaps without fully comprehending, the world fatefully decided to back the Zionist project, and set the entire sequel in motion, rather than choose some other conceivable, but not actually implementable alternative. In some sense the die had already been cast.
Morris, who came to prominence first for exposing the mythology of the Israeli founding, has since entertained the argument that the mistake the Zionists made was in not being more thorough in their ethnic cleansing, leaving intact the bases for strife, war, and the same general measures under even more difficult conditions. So, under a pessimistic or some would say simply realistic judgment, the choice for an Israeli is that choice described above, but not as an abstract assessment of ideal justice: Either decline to defend the survival of the nation, or accept unflinchingly the requirements for it, all of them. It may not be something we find we can continue to support, but our co-responsibility for it, the continued commitment to the Zionist project of large segments of our populace, numerous historical and other ties, and the existence of shared enemies and other shared material interests all make separating from the conflict on simple or supposedly simple moral grounds difficult or impossible.
Right. The problem, and one hesitates to say so, since even admitting of the possibility is blasphemous, is that such pieces on "settler colonialism" are written almost universally on the unproved assumption of a practicable alternative, rather than with cognizance of the unfortunately easily evidence-able proposition that it's still a settler-colonize-or-be-settler-colonized world, and even more immediately so in Israel's region, and for Jews in that region. Presented with the alternative of shame and survival, a people may choose survival, and discover ready resources for converting the cause of shame into a source of pride.