Why might religious people from Chaucer's time have been upset with Chaucer's view of the Monk and the way he described him in The Canterbury Tales?

In Chaucer's The Canterbury Tales, the author paints a less-than-complimentary view of "the Monk," one who has sworn to serve the Roman Catholic Church during the Middle Ages. The Church was the central authority at the time, with no separation between church and state. The Church not only made the laws that governed the people, but it also set the tone for the people's spiritual welfare. With this in mind, the Monk should have made himself humble, selling all that he had to give it to, and serve, the people. The Monk is one of several members of the clergy on the pilgrimage, although only the Parson is a true man of God.
In that the people completely supported and did not question the authority of the Church, many believers of the time might have felt Chaucer's writing was disrespectful. It is important to note that some people may have been aware of the Monk's behavior (or that of other clergy members in their parishes), however, and might have applauded Chaucer's exposure of these sneaky, greedy, and unethical members of the cloth. (Chaucer was a student of human nature; rather than creating problems, he wanted simply to describe the kinds of people he met in real life: those who were what they espoused to be, and others who lied and took advantage.)
Chaucer describes the Monk. The Monk was a man of venery (he had a deep love of hunting). He owned a horse, and the horse wore a fine harness (which was not cheap). By not living in a cloister, his time was not spent in service to others as much as it was spent following his own pleasures. The narrator sarcastically questions why a monk would ever spend time studying—to what end? What good would he do breaking a sweat?
Hunting was dear to his heart:

Therefore he was a rider day and night; Greyhounds he had, as swift as fowl in flight. Since riding and the hunting of the hare Were all his love, for no cost would he spare (25-28).

The Monk had greyhound dogs (known for their speed). He also had no qualms about spending as much money as necessary in his hunting exploits. He was, however, a man who was supposed to have given up his worldly goods and serve God's people.
The Monk wore clothes that were expensive (only the best for him): his cloak (fur-lined) was adorned with a pin—a gold love-knot. Why would a man of God be dressed in such expensive clothes, and why would he wear a love-knot pin?

I saw his sleeves were lined around the hand With fur of grey, the finest in the land; Also, to fasten hood beneath his chin, He had of good wrought gold a curious pin: A love-knot in the larger end there was (29-33).

There seemed little time or interest on the part of the Monk to serve others. Chaucer does not come right out and censor the Monk. He makes observations and lets the reader make his or her own decisions.
People of the time might have sensed criticism from the author; they might have resented what seemed to be fault-finding. Students of human nature (like Chaucer) would be able to identify the contradictions in behavior among many members of the clergy. Some might have seen these observations as a reflection of the Church's lost of control over its people, a poor reflection on the Roman Catholic Church.
At that time, the Church was in charge of every aspect of life. With those clerics in Chaucer's writings far outside the guidelines by which they were to live their lives, one wonders if they should not have been watched more closely.
https://www.owleyes.org/text/canterbury-tales/read/the-monk/root-218780-1