There are indeed a lot of dark marketplaces these days but I do not think that is wrong or something because its not bad and also not good of course.
Dark marketplaces cannot be stopped and there are more currency's used on it so...
As long as there are people who wants to hide themselves underground and doesn't want to have association with legal things. Dark marketplaces are going to exist. Different illegal trades are happening there and as long as there are monetary value involved they are going to remain and no one will ever stopped them for keep on going.