I consider booing the valorization of citizenship naturalization ceremonies entirely defensible, and Kristol's anti-American comment entirely indefensible (although not the most indefensible thing he's ever said.)
It never occurred to me that he had simply imagined it, but according to Mickey Kaus, that's what he did:
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The problem is that like many neoconservatives, Kristol regards immigration as literally sacred, and can't imagine that people coming to into the country are coming in for the wrong reasons. He might ask Benjamin Netanyahu.