As a payment network YES, Bitcoin is halal. In fact, Bitcoin goes beyond what more conventional closed banking networks offer. Unlike conventional bank networks which use private ledgers where there's no guarantee that the originator actually owns the underlying assets, Bitcoin guarantees with mathematical certainty that the originator of the transfer owns the underlying assets. Conventional banks operate using the principle of fractional reserve, which is prohibited in Islam.
Forgive me, Im Xtian so working from an outside knowledge of Islam. But would not the speculative nature of bitcoin make it haram, as for many it is essentially gambling? And that is aside from the dark market associations, as expressed by the OP.
I think it comes down to intent. Under Sharia, a lot of the same legal/fiscal structures you see present in other systems are still there, but adjusted to avoid usury and speculation. Finance needs certain features to function efficiently; these are present in Sharia finance in alternative forms.
If a bitcoin user is purchasing bitcoin to utilize the network as a payment system, he should be fine. But if a body purchases bitcoin purely with the expectation that the price will go up, that does indeed seem like a violation of the spirit of Sharia.
When its all said and done, the only argument that will truly matter is the one you have with the Creator about bitcoin!
