Dark net is just a tool, it is neither good or bad. Some of the things you cite as being bad aren't unilaterally bad. Drugs, for instance, can be powerful forces for good when used responsibly. Forged documents are quite a good thing when dealing with tyrannical governments. Even contract killings can be useful if used only in defense.
Just because you don't have a legitimate use for something doesn't mean no-one else does. The dark net provides anonymity, and anonymity can be incredibly important. Even Forbes recommends using Tor for anonymous submissions.