1. Obviously, I can´t WIN a discussion concerning a Universe controlled by the other participant. Pointing out that a given situation perhaps should have been clarified at an earlier point should not be a problem in itself.
2. Clearly, the GM does not understand the concept of REDUCTIO AD ABSURDUM, however adept he is at using it. It does not depend on anything being correct,it is simply taking your opponents argument and extrapolating it into absurdity, thereby turning it around. It´s a good trick, but it´s a trick nonetheless.