In effect, they would also be sending all their sensitive, potentially illegal traffic to be read and copied by the american NSA agency. http://en.wikipedia.org/wiki/PRISM_%28surveillance_program%2...
People proxying illegal traffic through the USA would immediately be "on file" in the US registered as dissidents, criminals, and potential spies vulnerable to blackmail from US agencies.
I can see CIA looking at how their propaganda are affecting foreign nations by seeing who reads it from where. Foreign nations could even see proxying subversive traffic through the USA as being a worse crime than the subversive traffic itself.
Think twice about using this.