The US government is not only currently the largest funder of Tor, but also are the people who originally invented the concept, and one of the implementers of the current version of the product was fresh out of the NSA when he implemented it. The US government likes Tor because it is used by dissidents in countries like China, Iran, Libya and many others to circumvent their government censorship of Western information sources and ideologies. They also probably use it to some extent for covert communications with assets in enemy territory and for hiding their own field agents communications back to them (this was what it was originally intended for when the United States military designed it). It is also an invaluable source of OSINT as they spy on exit traffic. They probably also use it to avoid attribution when engaging in cyber warfare and espionage, and of course to protect communication patterns between politically important people, definitely many embassy workers are required to use Tor to protect from spies (although this has backfired on them since they don't all understand that exit traffic isn't encrypted!). Also, many large corporations use Tor to protect from corporate espionage, law enforcement and military use Tor to gather information online without using IP addresses that can be tied back to government or military agencies, etc. Indeed Tor has many uses for them, enough that they spend millions of dollars a year in donations to the project. They however suffer from cognitive dissonance in that they see quite clearly that Tor protects dissidents in hostile governments, without recognizing that the people using SR and other hidden service sites, are equally dissidents protecting ourselves from a hostile government. Also the vast majority of Tor traffic is lawful in the United States. It's primary use is apparently downloading legal pornography (there are at least two studies backing this), a big secondary use seems to be getting around firewalls (for example maybe your university blocks traffic on a certain port when you use their network, so you can't access IRC on standard ports, but they don't block Tor or if they do they don't block bridges).