The couple I referred to are upstanding law abiding citizens, but are vocal opponents of the local authorities. Not having any legal reason to shut them up, an obscure dark-humor posting by one of them was discovered and used as a pretext for totalitarian oppressive tactics (break into home without permission or warrant, confiscate lawful personal possessions (worth several months' pay) without adjudicated reason). It's akin to if you made some joke about observing the NSA like it observes you, a dozen armed-and-ready cops broke into your house and confiscated all your computers/phones/etc without a warrant.

The more they know, the more they can act against you when they want to.

ETA: I, like many, hesitate to say certain things on any recordable medium because we have reason to believe everything is recorded (and that which isn't can be derived from metadata). While my example used public data, the practical difference between public & private (chat board vs. PRISM) is becoming moot, and the consequences involving oppressive government acting without warrant is exactly the severity we are concerned about.