Photo: Tom Fullum/Getty
A popular way to define religion, as well as other complex concepts, is to identify an 'essential' feature and say it is the defining characteristic. There are many problems with this, not the least of which is how it overly simplifies complex issues. Even more significant flaw is how it encourages people to improperly exclude from a concept anything deemed inconvenient.
In religion, for example, people will deny that something is part of "real" religion whenever they don't like it.