"logically possible world physically identical" "Point 2 is textbook begging the question" -> It is a thought experiment. He is proposing a possible postulat

"logically possible world physically identical" "Point 2 is textbook begging the question" -> It is a thought experiment. He is proposing a possible postulate to spur talking about the ideas. It isn't a 'proof'. Just like we don't argue with Schrodinger about the absurdity of a half dead cat.