Fiat seems like the best option for anything illegal, it is strange to me how the media continues to claim bitcoin transactions are anonymous or untraceable when the open ledger design of its system suggests the opposite.
It baffles me as well. it seems, like this is the agenda to portray the cryptocurrencies in the most shady way possible.
I mean when you think about it, it's a pretty smart way to try to delegitimize Bitcoin -- because if they can paint it as this crazy online currency that only does drug, gun, etc transcations then the public would be fine with banning it -- as they would simply think that it is a parasite to the world leeching off of drug users and hiding.
Cash is what people use to buy this stuff, it's easy enough and you have ZERO chance of getting caught just by using it (minus the in person risk)
So yeah, this is what governments do -- expected.