The NSA and the FSB want to puncture Tor anonymty and expose the identities of the people using it because the Tor browser erases identifying browser fingerprints.
Almost everyone who uses the internet has a unique traceable fingerprint.
An Internet user can check his or her own internet uniqueness in a few seconds with Panopticlick, a one-click test created by the Electronic Freedom Foundation (EFF).
Most people find themselves to be pretty unique; 1 in 4.5 million to be exact. Go ahead, try it.