It does not matter that Sedevacantism is not doctrinal per se.
It breaks.communion with the pope, and places men outside the church.
As pft said, the devil is laughing in hell.
Seraphim,
How does one break communion with the Pope, when there is no Pope at present? We are not breaking with a certain Pontiff, but one whose claim is rejected by many in the Church.
Your position, whether you admit it or not, also is a rejection of the Vatican II "Popes." If you truly believed they were Popes, you would accept their teaching and law, and would remain in communion with them and the bishops in union with them.
When one remains in communion with the Pope, they do not just give him primacy of honor, they submit themselves with docility to him as their Supreme Teacher and lawgiver. Catholics learn from the Pope as their teacher, and they trust the Pope as they know he could not lead them astray. There is no holiness where there is disagreement with the Pope. (St. Pius X)
So, when you say that Benedict XVI or John Paul II were popes, what does that mean for you? Did you learn from them? Do your trust the sacramental rites that they have approved or allowed to continue i.e. the Novus Ordo for example? Do you trust
all of their canonizations? Do you believe that the Church is irrevocably committed to ecuмenism, as John Paul II has taught? Do you believe that non-Catholic religions are a means of salvation as Vatican II and Benedict XVI have taught?
If you say no to any of the above, then you are not learning from the "Pope," or are not trusting in the laws given by the "Pope," to the universal Church. If you say "no" then you are disagreeing with the "Pope."
If you are disagreeing with the Pope as your Supreme Teacher as the rule of Faith, then what are these Popes to you? What is the point of a Pope if Catholics cannot trust his teaching given to the universal Church? What is the point of a Pope, when lay Catholics and priests can refuse to be taught by him and ignore his laws, and operate chapels outside of his jurisdiction?