No, the sedes have the correct view of infallibility, which is that a Pope is infallible when he teaches on matters of faith and morals to the universal Church i.e. in encyclicals, but not necessarily in speeches.
Read SJB's post above. Obviously, you do not have an adequate understanding of this doctrine or its practical application. Neo-Catholics (a legitimate term to describe Catholics who have adhered to all things new) have the same understanding of this doctrine at least in application as do the Catholic who concludes there must be no Pope. This is the common thread that joins the two extremes. One follows every word because it emanates from the "magisterium" the other rejects the person who possesses the magistracy because they detect error in the same medium. The whole thing turns on this notion, as well as the nature of the ordinary universal magisterium, which incidently, John Lane and John Daly have misunderstood as well, denying that an essential characteristic is extension in time, i.e. tradition. But it follows that if infallibility cannot be applied in practice to any of these statements, propositions or actions, the possibility of error remains, however remote. The remoteness of the thing shouldn't offend the taste for I fail to see how the remoteness of the possibility of the invalidity of a series of Pontiffs is any different.
Now if infallibility is removed from the equation, the only thing left is to demonstrate pertinacious heresy which even if accomplished amounts in the end to one's opinion. Anyone familiar with the history of theology will know that even the greatest, most learned theologians have disagreed as to what constituted an heretical proposition.
I certainly understand why some would be so scandalized by the Conciliar Popes that they feel compelled to conclude the vacancy. The problem lies soley in the fact that these same men desire to form their communion around this opinion, to make it quasi-mandatory. This is a serious mistake for the many reasons given in the past. This theoretical variety leads to even greater errors, most especially does it lead to sinning against brotherly love.
On the practical level, there is no material difference between a traditional Catholic who has refrained from discerning who remains a member of the Church whilst at the same time withdrawing, as per the command of the Apostle, to practice the traditional Catholic faith, and the sedevacantist. Morally speaking, the Popes have been absent for the last 40 years. I see no reason to venture into the canonical question.