The basic error of sedevacantism (the source of all other errors) is protestant subjectivism and the lack of distinction between material and formal heresy. Another mistake is dogmatizing every word of the popes (every word written or uttered by the pope treated as infallible), and also dogmatizing the teaching of the Second Vatican Council, which is pastoral, non-dogmatic.
Obedience to the pope is necessary for salvation - this is the dogmatic teaching of the Church (en.wikipedia.org/wiki/Unam_sanctam). However, one can never forget that the respect due to the pope is unconditional, while obedience to his teaching is conditioned by the theological rank of a given statement and has boundaries defined by the sacred deposit of faith (depositum fidei). If there was an obligation of unconditional obedience to every word of the pope, the Church would cease to exist many centuries ago.
Sedevacantism is a false theory, according to which the popes have not been popes since the Second Vatican …More