The Mortara case is interesting on several different levels. It’s one of the reasons the Jєωs hated Venerable Pius IX (A great man!)
I'm surprised that Wojtyla went ahead with the "beatification" of Pius IX after the howls and garment-rending from the Jєωιѕн quarter. I did read somewhere else, though, that they secretly relished this beatification because it would given them additional ammunition against the Church.
So, it was actually the case of Pius IX that made me reconsider my erstwhile dogmatic sedevacantism. I ran into a man who had decided that Pius IX was an anti-pope, a heretic. That gave me pause to consider whether this guy, or Father Cekada's infamous "Aunt Helen," could just denounce any Catholic pope as a non-Catholic anti-pope. There are a fair number of people who are starting jump on the bandwagon of declaring Pius IX an anti-Pope, therefore rejecting papal infallibility, and basically becoming Old Catholics and/or Orthodox.
What's interesting is that when Pope Pius IX condemned the Old Catholics, he accused them of rejecting the indefectibility (not infallibility) of the Church. He realized that it was a bit of a circular argument to say that they were rejecting an infallibly-defined dogma when it was the ability of a pope to infallibly define dogma that was being defined. So he teaches that the Old Catholics are heretical because their conclusion would mean that the Catholic Church had "gone off the rails" ... which is not possible given her indefectibility. That's why I keep saying that the core problem here really is indefectibility. People can quibble to a certain extent regarding the precise limits of "infallibility in the strict sense" (as Msgr. Fenton called it), but with the Conciliar Church we're not talking about a problematic statement in an Encyclical Letter, but the establishment of an entirely new theological system, system of worship ... in short, a new religion that, were this change attributed to the Catholic Church, it would be tantamount to a substantial corruption of the Catholic Church, making it unrecognizable as a religion to Catholics who lived and died before Vatican II, and therefore lacking the notes or marks of the One True Church founded by Christ. That is the problem here more than the precise legal disposition of a heretic pope.