I think that the ideal way of working for mixers would be for them to try to find a balance between offering their service to everyone, but with a move away from those funds that come from publicly denounced illegal actions, which then cause them to get into trouble.
The huge money they make is from these publicly denounced illegal sources. How will they balance this?
I would not agree that most coins come from
"bad sources", because if that were the case, the pressure on all mixers would be much greater, and that would result in the fact that we would most likely not be able to publicly discuss them here. Most of those who use them do not have bad intentions, their only motive is to protect their privacy.
The authorities are not so interested in the fact that an individual buys BTC and then sends it to mixers, but that the bad guys launder huge amounts of money from hacking and scams through it.
Total privacy doesn't differentiate between these two. A notorious criminal might claim they are just security their privacy. Mixers making more moves to differentiate will at a time contradict the purpose of their existence.
A criminal cannot be in the same position as someone who legally bought BTC, because he is in the position of wanting to hide the origin of the coins he acquired illegally, there is no justification for that. As far as I know, no mixer has publicly announced that the purpose of its existence is to be a service through which criminals will pass stolen funds in order to launder them.
I was just thinking of a way that would enable them to divert the attention of the authorities from themselves - if of course it is not something along the lines of what you mentioned, in which case it is easier to let things take their course.