I don't understand. If it is a usurpation of authority to say that someone has to agree with your opinion in order to be Catholic, how is Fr. Jenkins not doing exactly the same thing when he says that dogmatic sedevacantists are not Catholic because of what they believe? How is he not usurping authority in deciding who is traditional Catholic and who isn't?
Uhm, he did not say they are not Catholic, but that they are not TRADTIONAL Catholic. To my knowledge, he does not refuse the Sacraments to people from dogmatic sedevacantist chapels ... unless there's also a question of the +Thuc line, but that's for a different reason (that I don't agree with). One would have to ask him precisely what he meant by that, since the term Traditional Catholics has about as many definitions as you have Traditional Catholics.