We paint ourselves in a corner when we claim infallibility for ourselves. The teaching of original sin is that sin has so marred our core that we are dead and can not respond to God such that it takes God to come to us in mercy and revive our mind and heart for us to come to him. This teaching does not deny that man can pray, read the Bible, do good deeds that is not what is meant. It means though that all works of righteousness are filthy rags in God's sight. It would be good works done from impure hearts. Man does not only need help, he is spiritually dead that he needs to be resurrected in spirit.
The practical outworking of original sin (as I see it) is that it keeps us on our toes. Original sin is not done away by conversion, it inheres in the believer. The unbeliever is sinner only but the Christian is a believing sinner (he is both sinful and holy at the same time). It is a safe teaching that helps the Christian not to value himself highly than he should.
The RC teaching of Papal/Magisterial Infallibility is not practical and flies against the teaching of Scripture - that men are liars. It does not see the possibility in practice that they can be led astray by their leaders. RCs always believe the the RC magisterium will always be guided by the HS, no matter what happens. What about Acts 20:26-30?
The RCC paints itself in a corner when it attributes something to the hierarchy what is meant to be attributed to God, like infallibility. This I think, is the reason why there are Sedevantarians who believe the RCC has betrayed Council of Trent and Vatican I. Put it this way, if in their hearts they believed they were wrong in excommunicating the protestants, through the Council of Trent, they could not simply retract their damnable pronouncements. That would mean they are not infallible as the doctrine says. So what to do? Just redefine the meaning of words and come up with Vatican II. More inconsistency. When you are infallible, the command to repent is not applicable to you. This locks you inside a room whose keys no knows what happened.
It is like falling on a quick sand, the more you move, the more you sink. It is a shot in the foot - as some say.