US Government Overreach on BTC?

How is the US govt able to require BTC providers to identify to whom I send BTC? BTC is not a US-regulated currency. Is this not an illegal search I am protected from by the US constitution? Seems like some of the Know Your Customer requirements are illegal in the US yet the US is requiring BTC providers to comply. Something is wrong here. I am choosing to transact in BTC because it can do things with it the USD cannot. I should be free from US government prying with regard to who I send BTC to. They may be able to oversee and regulate purchases I make with USD, but that should not extend to BTC transactions I send.

Thoughts?