Because the Article I, Section 8 says that Congress has the power to:
"To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;"
"To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;"
Actually, it is Congress. Specifically, the Court ruled that the use of bitcoins for the transactions at issue does not (as the defendant attempted to argue) cause them to fall outside the scope of the Exchange Act of 1934.
As I had to explain the difference between lunch and arbitrary use of government power, do I also have to explain the difference between government of consent and tyranny?
It's not your fault; this is just a really terrible venue for political discussions.
The overarching power of government is the problem, not how we discuss it on the net.