I am not sure why Kenneth Burke calls "piety" what I have been calling "decorum." I remembered the passage below quite well, but misremembered his terminology. I had thought he had used the word "decorum" but he doesn't:

Refined critics, of the Matthew Arnold variety, assumed that exquisiteness of taste was restricted to the "better" classes of people, those who never had names ending in "ug." Yet if we can bring ourselves to imagine Matthew Arnold loafing in the corner with the gashouse gang, we promptly realize how undiscriminating he would prove himself. Everything about him would be inappropriate: both what he said and the way in which he said it. Consider the crudeness of his perceptions as regards proper oaths, the correct way of commenting on passing women, the etiquette of spitting. Does not his very crassness here reveal the presence of a morality, a deeply felt and piously obeyed sense of the appropriate, on the part of these men, whose linkages he would outrageously violate?