Association with darknet markets seems to get a lot more attention. Something also tells me that mixers aren't doing the sort of taint analysis that Chainalysis or Ciphertrace does.
If I were operating one I'd be keeping an eye on the hottest addresses. It's almost inevitable they'll pay you a visit.
Aiding privacy and allowing druggists to get by is fine by me. No way would I want my service to allow known thieves to get away clean but that's me.