The following 12 arguments made against sedevacantism have a flip-side, which works against the one making the argument. The purpose of this work is not to refute or give credence to the argument. It merely shows that sedevacantism exists precisely because the flip-side of the argument actually came first.
1. Argument: The Church can’t go 60 plus years without a pope.
Flip-side: The Church can’t go 60 plus years with heretical popes.
2. Argument: The Gates of Hell have prevailed if the Vatican 2 popes aren’t true popes.
Flip-side: The Gates of Hell are running the Catholic Church if the Vatican 2 popes are true popes.
3. Argument: Theologians said universal acceptance makes for a true pope.
Flip-side: Theologians say heretics can’t be popes.
4. Argument: Sedevacantists are divided over which popes are true.
Flip-side: Novus Ordo Catholics are divided over dogmas of the Faith.
5. Argument: Apostolicity is only found in bishops with ordinary jurisdiction.
Flip-side: No one in the Novus Ordo religion has ordinary jurisdiction.
6. Argument: Sedevacantists haven’t elected a pope.
Flip-side: The Novus Ordo religion hasn’t elected a pope who’s Catholic.
7. Argument: Sedevacantists privately judge that there’s no pope.
Flip-side: Novus Ordo “Catholics” privately judge that their popes err in good faith.
8. Argument: Sedevacantists reject the teachings of theologians on universal acceptance.
Flip-side: Novus Ordo “Catholics” reject the teaching of theologians on what makes a person a formal heretic.
9. Argument: Sedevacanism is a form of Protestantism.
Flip-side: Protestantism is revered by the Vatican 2 popes who promote and uphold Protestant beliefs.
10. Argument: Sedevacantism didn’t exist until the 1960’s.
Flip-side: The Vatican 2 religion didn’t exist until the 1960’s.
11. Argument: Sedevacantists have left the Church.
Flip-side: The Vatican 2 religion left Catholicism.
12. Argument: Sedevacantists reject Vatican I’s teaching on perpetual succession after Peter until the end of time.
Flip-side: The Vatican 2 popes reject Vatican I’s teaching: a). to reject and condemn [all] the errors contrary to Catholicism. b.) that the “meaning of the sacred dogmas is ever to be maintained which has once been declared by Holy mother Church, and there must never be any abandonment of this sense under the pretext or in the name of a more profound understanding. May understanding, knowledge and wisdom increase as ages and centuries roll along, and greatly and vigorously flourish, in each and all, in the individual and the whole Church: but this only in its own proper kind, that is to say, in the same doctrine, the same sense, and the same understanding.”
Speray's Catholicism in a Nutshell 
Short, sweet, and to the point.
Not much debating going on here. Nice job Steve.
Yeah, there are definitely counter-arguments, and a lot of anti-sede arguments at times don’t seem substantial. Sedes should self-critically look out to make sure their arguments hold as well! As well as maybe also do more to prove/disprove conclavism, sedeprivationism, Siri-esque theories, or other alternatives that are floating around in competition with Catholicism (for, although the Vatican 2 “popes” may not be popes for instance, that wouldn’t logically imply there is no pope, but there could be a conclavist pope, or a “hidden” pope somewhere, or that such “popes” are “material popes”, as these arguments assert, and I’m not sure if other such arguments have all been attended to)
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