But for that we have mixers.

We have mixers and CoinJoins, sure. But we also have exchanges that freeze coins that originate from known mixers, casinos, and whatnot. I expect this is going to become a trend in the future. Regulatory pressure will force centralized exchanges to consider funds that came from such services as being dirty, illegal, and laundered. You will be asked to prove that you are not a criminal and not the other way around. For that reason we have decentralized exchanges...until they find a way to blacklist those coins as well. When and if they do that, we are left with face-to-face deals.