As a layman, that makes perfect sense. As a lawyer the story might be different. We all know that it's not entrapment as long as the police get a camera crew to entrap for them. A popular TV show was based on exploitation of that.
If someone burglarizes your house, is your neighbor's security camera footage unusable because it was gathered before a warrant? Isn't a private security camera's intention to capture someone doing something bad, just like Flock?
"Thus it is government surveillance prior to a warrant."
But it's not any more than your home security cameras are "government surveillance prior to a warrant". It's the overwhelming degree to which these cameras are deployed that is offensive, similar to how Ring doorbell cameras used to inform police was offensive. Everyone hates this, but your assumption that the law supports your point of view is naive. Of course Flock exists to exploit the public through law enforcement. But that's not new or interesting.