Sanguina Cruenta
Does that make sense with Catholicism? I thought in Catholicism, the correct beliefs were spelled out, or at least the parameters given. On matters of doctrine the Pope is infallible, etc, and papal infallibility is an aspect of being Catholic, so believing the church was wrong on a particular issue would probably be some sort of sin of heresy and you'd have to confess it. On the other hand they consider you Catholic even if you leave; you're just lapsed... sin is just a sin. You could play football with baby corpses and still be a Catholic just fine, you'd just be a terrible sinner. It'd probably even be OK depending on the nature of the baby corpses and the time in history in which you kicked them.
But today, be you doubter of papal infallibility or baby kicker, your sins are equal in the eyes of god, aren't they?
Wandering thoughts...
Infallibility isn't universal. A Pope is not always speaking ex cathedra, and the Church freely admits that not everything he says should be considered so. Popes are subject to error, sin, and personal opinion the same as the rest of us.
There are also large sections of the church throughout its' history that have denied papal infallibility entirely - all of England and Ireland through large swaths of the 18th and 19th C. come to mind - and don't consider it an article of the Catholic faith. It is a matter, instead, of Church doctrine and dogma, and is more politically-motivated than religiously. Not believing in papal infallibility is not a sin.