How does this relate to Mandeville? There is a sort of blind acceptance between church and followers, which stems from both the Pope and the bible itself. Take the reality show, "19 Kids and Counting". This is a family that has become so huge because of the belief that God advocates for having as many kids as possible. Why do they believe this? Because the Bible said so, so it must be true. While this may seem outlandish, and something to scoff at, the fact that they have remained on television for so long shows that there are people who eat up the spectacle, as well as maybe even believing in it as well.
Another example is the Westboro Baptist Church, which advocates that everyone is going to hell. They, as a church, demonize soldiers, members of the LGBTQIA community, liberals, or anyone not like them as not fit to go to their heaven. This could be directly related back to Mandeville, where places or people that were considered "bad" were either badly described, othered, or simply told to be "not good and that you should never go there". In both cases, there is a need to paint differences as grotesque and wrong in order to prove that You, as the church or as Sir Mandeville, are in the right. The excuses for such are the same too; it all boils down to acceptance from God as a way to whitewash discrimination as righteousness.
So, the attitudes of "The Pope/the Church/ the Bible/ God approves my message, therefore it is right" is far from being just a medieval attitude, as there are still existing social movements happening today that capitalize on it. And while we might have some more progressive thinkers in power right now in the Church, the next Pope may bring us back to medieval thinking again.