Non-Catholics do not matter.
This is an assumption and a rather unfair one I'd say.
Look all one can say is that there is no universal and peaceful acceptance.
Translation: Please, just let me assert my opinion in peace and don't bother me with any inconvenient details.
But if you are dealing with a bunch of non-catholics, then you can safely say that no valid proof could every be had again. Wait, unless you mean that we can witness a peaceful acceptance when the
sedevacantists all consent to an election? Are you implying that you and those who share your opinion constitute the true Church? If so, why don't you simply elect your own Pope? Why not bring an end to this confusion? Have you no concern about the common good of the Church? Why do you profess to be a member of a body without a head? Would that not mean that you are a member of a corpse? Does this imply that sedevacantists are impotent in electing the true Pope? If so, how does that square with the implication that you and yours constitute the true Church? For the true Church is a perfect society that has within itself all that is needed to attain its perfection. This is most certainly not how true catholics would behave, you should be ashamed of yourselves.
That doesn't prove B16 is not the pope...it just doesn't prove that he is. That proof (that he is) is just missing here.
John XXIII, Paul VI, John Paul I, John Paul II and Benedict XVI were all peacefully recognized as legitimately elected Popes. If a moral unanimity suffices, then a few detractors couldn't really cast any doubt upon this proof.
It is erroneous beliefs about the nature of the papacy and heresy that cause otherwise strong resistors to say he is a true pope. They simply ignore him and then claim this is a possibility...for a body to avoid it's own head.
Please detail precisely these errors and heresies, give examples in the form of explicit propositions and the surrounding context which establishes intent and meaning.