Some things that people dislike about Flock:

Flock has had a a number of security issues where people have demonstrated that the cameras could be accessed easily by anyone because of (IIRC) the use of default passwords.

Flock have said that they weren't doing this or that (I don't recall the exact details, I think initially they may have said it was just recording license plates), but then people found out they were doing a lot more than that.

Flock and police departments have been found to have been doing way more than using the cameras to investigate crime, including stalking friends and lovers and exes, and in one case one of the guys was found to have been regularly watching a young girls gymnastics gym a lot.