Directly, "the thin blue line" expresses the idea that the police are what separates society from chaos.
It doesn't inherently suggest police are justified in acting outside the law themselves, though, of course, various people have suggested this (interestingly, from both a pro-police and anti-police perspective).
It seems obvious to me that the post was using this phrase in the sense of being a thin shield from chaos.
Directly, "the thin blue line" expresses the idea that the police are what separates society from chaos.
It doesn't inherently suggest police are justified in acting outside the law themselves, though, of course, various people have suggested this (interestingly, from both a pro-police and anti-police perspective).
It seems obvious to me that the post was using this phrase in the sense of being a thin shield from chaos.