That is single handedly one of they most arbitrary ideas i have ever heard.
I got that from here. (a must read by the way)
I took art history in college and one lecture the prof was going off on how the masters from the renissance weren't "honest" (or something else stupid) enough because they pained religious themes instead of more "progressive" subjects. I reached my limit of her idiocy and said that they were really just sucking up to the Pope and using him for money. She was like "Exactly! blah blah blah..." Everyone was trying not to laugh.