Why did Longstreet not want to go through with Lee's plan at Gettysburg? He thought the Union position was too strong.
He did not believe his men could get into position.
Longstreet did not know the terrain.
He did not believe Lee was a capable leader.

Chaucer was clearly disenchanted with the Catholic church and uses a lot of satire in his tales, definitely.  One way many authors "got away" with criticizing the church was through satire, which involves poking fun at serious subjects.  Chaucer is no exception.  I do not believe that he had very specific purposes but that he wanted to merely bring attention to some of the inadequacies and wrongs in the church. 

He may not be saying that they are "liars" in particular, but he absolutely thinks of them as corrupt and deceptive. 

Nun seems flirtatious and too much involved with appearances to be holy.

Monks are materialistic with his hunting dogs and horses, fancy clothes, and no time for studying the good book and the rules of St. Benet who said monks should be impoverished, chaste, and obedient to God. 

Friar seems to be bribing young ladies to give him sexual favors and then finds them, husbands. He knows the taverns and inns better than the poor whom he is supposed to be serving.

Pardoner--cons people into buying holy relics that are frauds--the pillowcase he said was Mary's veil,  the cloth he said was part of Peter's sail, etc.

Summoner--appears to be a drunkard and his carbuncle-covered face suggested in Chaucer's time that he was a lewd and lecherous individual.  He also puts on airs with his very limited Latin.