You're probably being rhetorical....but.....
The ends justify the means.
The government stands down while officers are killed, then the government tells the sheeple that the government needs to take away some liberties in order to provide better security, then the government repeats the cycle resulting in an erosion of individual liberty.
What did the federal government do in Ferguson? The government didn't investigate the perps, they investigated the police.
What did the federal government do in Balitimore? In this case the local government encouraged the mayhem while the feds investigated the police.
What did obama do during the "beer summit", during Ferguson, during Baltimore, obama blamed the police. Don't think that people don't see this and decide they don't have to follow the rules and that it is OK to shoot at the police. Classic communist tactics, terrorize the subjects into giving up their freedom in the name of security.