Selil and Jedburgh's points about critical nodes notwithstanding, you can attack either the critical node or a critical circuit (nodes and connections) in a loosely coupled network. Even more importantly, you can induce "noise" (think of rumour in a social network) or feedback (think truly viscious rumours) through a network circuit that can damage or destroy it. In a tightly coupled network, you can do the same thing by accelerating a circuit vector. For example, you can take an orthodox belief in a social circuit and then put it on steroids - "everyone must believe X or they will be killed", etc. A biological analogy would be poisoning someone with overdoses of vitamin B.