There is a huge difference between a communication platform that some users abuse for illegal purposes, and a platform whose primary purpose is a marketplace for illegal goods.
Actually the marketplace was just a marketplace, it then was primarily used for illegal goods. It hasn't really ever been proven that it was setup as a marketplace for illegal goods.
I mean I would agree regarding the user base, but it was originally built as a utopian concept for a free trade of goods, akin to the original world of warcraft marketplace.