I don't think you seriously believe the NSA is trying to trawl for copyright violations. Arguments require more than just conflating some random facts and going 'there, see'.
They definitely are. Snowden literally proved this. They are collecting data at a MASSIVE SCALE. They are doing this as one of the commenters noted above; To find TS leaks and to find the next 9/11.
But they are logging that information in some database somewhere. So it's not a question if they care/ will enforce it now, but rather will they care or enforce it for the rest of eternity.
What people don't seem to understand about privacy is that once you give it away, it is gone forever. In some dystopian future where every American is assigned a social score, you pirating things in the early '00's may harm your ability to get a house loan.
The widespread adoption of TLS means that a far greater effort has been put into exploits needed to gain access to the unencrypted side of a communication channel. It's not as big an if as it was before Snowden.
Correlation attacks only work when you can see both ends of the traffic. When you visit an .onion address, there is no other “end”—all traffic stays within the Tor network and goes directly to the hidden service server, which is ‘just’ another relay within the network.
I would assume that the NSA runs enough TOR nodes to correlate traffic from one side of the network to the other side at least a decent percentage of the time. I would also assume that they have a realtime view of the number of bytes entering or leaving any datacenter.