It is not necessarily a bad idea, it's just one of the ideas. IIRC Ruskin, a leading art critic in 19th century, argued that art (aka paintings) should be mora

It is not necessarily a bad idea, it's just one of the ideas. IIRC Ruskin, a leading art critic in 19th century, argued that art (aka paintings) should be moral and Christian and I'm pretty sure at least a few really clever medieval and ancient guys shared the same notion (albeit their ideas of morality were probably different). But it's not a universally accepted truth. Just one of possible interpretations I guess.