Traceability and Anonymity aren't antonyms.

This fact comes up with Bitcoin a lot. I and everybody else doesn't know who a random hash is but all the activity involving that address is highly traceable. So all you need is an oracle (like a cryptoexchange) that can convert a hash into a person to enforce any penalties against a person.

Same could be true of the internet. You notice illegal activity from a specific IP; that source is responsible for that activity (they did it!). In general that IP is going to be some intermediary (like an ISP) who was relying a packet from a different IP so it'll be on them to provide the next person who is accountable and do you do this chain until you get to an end subscriber. Everybody is anonymous by default but can be traced back to an actual person.