The problem is that a private company holds onto the data forever. Then the government can ask the private company for that data without a warrant. With the number of Flock cameras (I'm upset at how many have popped up near me), it's turning into a record of all of your movements. And that record lasts forever and can be queries at any time.

You mentioned "more serious crimes", but what about the case where LEOs in Texas track women who go to get an abortion in another state? Or police officers who stalk their exes? Or an oppressive government that wants to know who went to a protest? Once the tool exists you can't assume it's only going to be used in a way you like.