If AWS maintained private infrastructure that stored and indexed data associated with people's license plates and vehicles and then charged customers to do searches against that data then yes, you could write them to ask them to purge data pertaining to you.

If Flock was just an opaque cloud storage service for law enforcement to back up their mass surveillance to then sure, your argument would have merit; it's not, it's a giant database of photos, locations, times, license plate information, and likely a lot more. They're not selling cloud storage, they're selling (leasing?) surveillance devices and tools.

The argument you're making implicates way more than just Flock, and is in a practical sense novel. If you can cite jurisprudence (or even legal experts) backing it up, I'm interested in reading it. Otherwise, I'm happy to accept that we just have premises about the law that are too far apart for an argument to be productive.

My experience on HN is that these kinds of discussions almost immediately devolve into debates about what people want the law to be, as opposed to what it actually is.