My opinion was that these services owners were unmoral persons who made profit thanks to criminals, murderers, drug cartels money lauderin wishes..
What use would a murderer have for a mixing service? And drug cartels traditionally have a slightly higher turnover than the average mixing service can handle.
It's sensible to cut the link between your coins and their past.
Well some mixing services have 2000 up to 5000 btc which is an amount much higher than any hitman can ask for doing his dirty job.
I am not placing links to such services from the dark net as it's against my moral values, but what I want to say I have seen such services in the deep web asking for 3000 USD prepayment and than 25 up to 5000 USD when they finish the job. It doesn't seem to me that these persons don't need mixing as this value is up to 82 btc the most.
For drug dealers I don't think they use bitcoin in such a massive way yet although I know there are some of them using it.
Bottom line is, mixing services are always useful mainly for privacy but some people like criminals can use them for their dirty intentions.