> you're pretending that a Jewish state isn't an ethnostate by definition
It isn't. Certainly not in a way that requires ethnic cleansing.
What definition are you using? Are all Arab states ethnostates? What about monoethnic countries [1]?
> Ethnostates are very very bad
Because they arise from ethnic cleansing. Nobody has a problem with Egypt or Finland being monoethnic, and I think it would be incorrect to call them ethnostates.
If Egypt and Finland (and Iceland and Palestine) are ethnostates, then we've broadened the definition to where they seem to be fine.
> it doesn't matter who's a "true" member of the group; it matters only that there is a group
Of course it does. If you can expand the group, you don't have a problem. The very act of nationhood is an exercise in defining groups of people.
One can have a liberal, democratic, Jewish state that isn't an ethnostate. Nothing about Israel's existence requires ethnic cleansing. That's just a weird own goal that argues for it.
[1] https://en.wikipedia.org/wiki/Monoethnicity