If you're not going to see what people did on a site, what's the point? Presumably nefarious stuff like pedo rings and dark markets will not stay in the same place very long.
At the same time, people can see what kind of politics you're into. Or porn. Or dating. Which is not terribly useful for the public interest, but you can see a cop abusing this for personal gain. I think Snowden mentioned his colleagues used to stalk their exes.
Also, anyone who's accidentally left WireShark open will know how much data you're sucking up. It's not actually a small amount, and it compounds if you're an ISP. And it sure isn't easy to filter huge pcap files, which you'll have to do if you want to find something specific. And then you have to glue the clues together, totally non trivial.
Last, how will this be used in court? Knowing what sites someone visited is not evidence they did something. Some guy visits an ISIS homepage, is that because he's curious or he's getting bomb manuals? At best you can use it to suggest some guy is a sympathiser, when he might well not be.