New religious movements are "free" to call every other religious group out over perceived errors and to posit their own set of "truths". The trouble starts when a new religious movement starts to formalize its various teachings into "the way" and/or "the truth". With the passage of time, the movement becomes less and less able and/or willing to subject its own formalized teachings to the same scrutiny they reserve for all other groups.
This is the predictable cycle found in religious movements down through time - especially those who set themselves apart from all others. It was as true for Luther as it was for the Anabaptists and as it is for the Amish, Mormons, Adventists, Christadelphians, Exclusive Brethren and JWs, among others.
It underscores a principle of ageing: The younger you are, the more flexible and adaptable you are, but with age comes a kind of cranky stubbornness and refusal to change your ways.