So, between all that, I think you're dramatically overestimating how effective both police and surveillance dragnets are. ;)
https://en.wikipedia.org/wiki/Clearance_rate
I want to expand on your point about privacy by pointing out that arrests are often entirely up to police discretion. A suspended license could result in a warning, a ticket, or an arrest; ultimately, it comes down to whether an officer is in a good mood when he stops me or whether he likes my face. Allowing surveillance dragnets just makes it easier for law enforcement to have something to charge you with if they don't like you.
More in my area or classified as missing persons to make murder rate look lower. Common trick in a lot of places, esp small towns. Yeah, clearance rate is a great measurement showing how often crooks get away with stuff. I didn't think of that now obvious piece of data. :)
" it comes down to whether an officer is in a good mood when he stops me or whether he likes my face. Allowing surveillance dragnets just makes it easier for law enforcement to have something to charge you with if they don't like you."
This is true. We already see that in some U.S. states and European countries. There are all kinds of BS laws on the books. The cops or courts want money. So, some percentage of people are pulled over with an assortment of "violations" to use against them. Troublemakers might be hit with a more serious version of it. Especially can be used to squelch dissent or activism.
Aaron Schwartz is a perfect example of the power prosecutors hold in a given situation. Because of who he was and his crime, they decided to go all out to set an example of him rather than keep charges lower or ignore it given students were supposed to have access. Discretion can make or break a person's life.