This coin mixers are used to hide transactions made from deals like drugs and child pornography or any other crimes. And nothing else.
Prove it. Prove that mixers are used only by criminals and nobody else benefits from them.
In the modern world it's you who has to prove that somebody is guilty, you know that, right?
And when you'll actually attempt to do that you'll understand how wrong you are and how pointless this (yet again) topic is.