Sorry but this is fake.
Show me a single link/article saying a mixer froze the funds because it was sent from a scammer.
Mixers have been mixing very large transactions coming from hacks (the Twitter hack as the latest exmple), or whatever. Why didn't they block the bitcoins so.
Why mixers are more and more actively used on dark markets?
If a mixer starts to do this, it will lose its reputation the next day. What you say is a real shit
-1: You don't want people to know how many bitcoins you have on your wallet
-2: You don't want people to know the address 1abcdefghijkl is owned by Oshosondy
-3: You don't want people looking at spending patterns
-4: You don't want to know the address owner of 1abcdefghijk is leaving at 123 avenue of liberty 75000 New York and to see people visiting you at home to kidnapp you. (similar story happened before)
As you say Bitcoin transactions aren't anonymous, this is why we use to say "pseudo-anonymous". Above are couple examples you can think about