Abuses and Vulgar Customs
Whenever anything is taken to an extreme, it produces abuses; once abuses arise, they will eventually develop into vulgar customs.
For example, Confucius spoke of filial piety, sometimes with a rigidity that was itself a flaw. This abuse, carried to an extreme, produced the vulgar custom of foolish filial piety. The story of lying on ice to catch a carp, if one thinks about it carefully, reaches a level of foolish filial piety that deserves criticism. Yet today, on the streets of Beijing, propaganda posters still promote such foolish filial piety, and elementary schools still teach such stories.
Wang Xiang's mother wanted to eat carp in the depths of winter. Out of filial piety, Wang Xiang used his own body heat to melt the ice, then caught carp through the ice hole for his mother. Is such foolish filial piety truly worth promoting? Besides body heat, there are many ways to break ice—smashing it with stones, lighting fires to melt it, and so on. Using one's body to melt ice is utterly ignorant and extremely harmful to one's health. Moreover, I strongly doubt that such a foolish method could actually melt the ice; this story looks more like a fabrication.
The abuses of Buddhism are likewise countless; after a thousand years of development, they have hardened into extreme vulgarities.