Next time please think a bit more before taking the dark web trolls words as a fact, what do you think BitMixer.io is doing? they don't have a secret program to do their mixing however they have their own automated system but it's not about being open or closed sourced as if you send your bitcoins to an open sourced mixer you never lose your coins? it's about credibility and trust not how it is executed.
It's not about how It is executed ? how could you tell for sure that BitLender for example is not logging the users information's for later use ? you don't. An open source project will add 100% trust , credibility as you could compile the source yourself and use it without worrying much.
I don't see what's the darkweb has anything to do with this because as long as you can actual browse the source code , then I see no problem here.