You have to look at it not from the perspective of a black market site, but from the perspective of anonymity. Sites operated on the TOR network are supposed to be anonymous which is a valuable contribution to the existence of free speech. The freedom of a country that outlaws acts between consenting adults can be debated, but there are many countries that are undeniably oppressive. If the US government can track down an anonymous site, then it is likely these countries can too.
Arguably anonymous sites can harbor truly dangerous crimes like murder for hire, pedophiles, and terrorists. However, they can also protect political activists and whistle blowers. So while this isn't necessarily a cut and dry issue, it is much more complex than just saying these are black market sites so who cares.
Arguably anonymous sites can harbor truly dangerous crimes like murder for hire, pedophiles, and terrorists. However, they can also protect political activists and whistle blowers. So while this isn't necessarily a cut and dry issue, it is much more complex than just saying these are black market sites so who cares.