Dear Qwerty,
If you make up the subject, (Is the Rebbe perfect?) you can’t require the other party not to dodge. Being that this is not a subject on Chabad, he is entitled to think it has no bearing on the matter.
The Christians are not non-Jews because of your classification. It is because they classified themselves as out of Judaism. It gets very muddy when we want to exclude those who think they are included. Unless you convince him to leave or return because of your argument, you are waiting for him to leave on his own. Unless you can come up with some hard and fast rule for what makes one a Jew. There was major debate in the last century on just this issue. Nobody settled it.