Bitcoin will be used for good as well bad things the same way it happens for several years with fiat, soo nothing new here, besides its harder to trace the people who are under the dark marketplaces.
Indeed you are right but I think its logical because every currency is used for some criminal activity these days and we can do nothing about it too.
I think its logical and not bad that it is used for it because we cannot do anything about it, it may even give the bitcoin a boost.
of course it is a natural thing and very logical if one uses currency bitcoin for something they need, whether it's illegal or legal is up to them, the difference with another currency bitcoin is more secure and hidden, that's why I see a lot of issues who came on this matter, I think it is not a problem right ?