The substance of the issue is that the sovereign country of Palestine has been invaded by fascist ethnonationalists (zionists) who have committed a genocide against the indigenous Palestinians to steal their land and establish a settler colonial entity. To say "israel has the right to exist" basically signals to everyone that you are fundamentally ok with the settler colonial invasion and genocide. Its simple.

That there can be no Israel without apartheid is the point. That Israel having only the right to exist if it is an equal state and therefore not having a right to exist at all is the point.

You would already be pro-genocide by using this paradox because this is exactly the type of flawed doublethink that liberal zionists use to justify the zionist entity's continued existence as a settler colony. "Israeli" liberal zionists themselves say this ("we should still exist but Palestinians need equal rights!") while happily living in someone's stolen home and serving in the SS.

Furthermore this is just a rationalization for some liberal zionist accepting a liberal zionist framing of an invasion and genocide. You can skip this whole set of mental gymnastics and just say "no I dont believe in settler colonial ethnostates so israel does not have a right to exist" or something similar and then go off on their genocidal crimes against the Palestinian people before the copers start playing the "antisemetism" card.

Sometimes you need to have a backbone otherwise you just legitimize and manufacture consent for genocide on live television. But to be clear at this point the guy is a liberal zionist who doesn't really care so its not really a problem of having a backbone.