We don't have to look far for examples of great teachings that have been twisted into bad practices by unscrupulous people. How is it that we fight religious wars, when all of the world's greatest religions preach pacifism? It is because beliefs are powerful, and ruthless people are eager to usurp that power for their own selfish purposes.
It is therefore useful to identify all of the ways that a belief system can get off track. Just as the principles and practices of science include ways of detecting bad science, the tenets of a belief system that is to persist must include ways of spotting false prophets and improper interpretations of the teachings.