By violence I mean physical violence. They don't have a right to (nor monopoly on) physical violence. Whoever holds that power is called the state - the neighborhood association can only request the state to act on its behalf, not order it. Also, some of the association's rules may be invalid, if they contradict the laws of the state. They are then unenforceable, even if you've agreed to them. They are superseded by the laws of the state.