Well there is no if. It was absolutely created illegitimately. That is what this whole article established. But the point is not that they should now disappear. The point is they should keep that in mind before acting like they're so justified in committing mass murder.
Regarding why no one is discussing the legitimacy of the US. The US isn't still holding a whole group of people under subjugation. Of course the way the US was established was illegitimate, the big difference is they don't deny it lol. Israel does.