Basically the entire point of the fourth Amendment (and sort of the Bill of Right as a whole) seems to be based on the assumption that we cannot trust the government to not abuse its power, so we purposefully limit its power. At least that's the impression I got, IANAL disclaimer I guess.
If we cannot safely assume that every cop is above-board, which we obviously cannot, then it's trivial to come up with cases of "if you got nothing to hide you got nothing to fear" defense. A bad cop could use Flock to stalk an ex-girlfriend. A bad cop could find some unsavory-but-not-illegal behavior from a politician (e.g. visiting a porn shop) and blackmail them. A bad cop could, as demonstrated by this article, simply use a Flock camera to harass someone they don't like.
I didn't think this was a controversial opinion, but I do see a lot of Flock/mass-surveillance defenders so I guess it is.