It actually isn't clear what Blackwell is arguing for, besides delegitimizing millions of people based on their ethnicity.
The Palestinians certainly have no magical right to their own state. Ethnicity does not derive a right to a state. But unless one rejects the values that America is founded on, people have a right to be citizens of the state in which they live, except in very temporary situations. Does Blackwell mean for the Palestinians to be citizens of Israel? Or is he rejecting American values for the kind of Apartheid system that South Africa had temporary success in running?