Cash is used to scam people. Should we make that illegal? Encryption is used by criminals. Why isn't that illegal? The internet is used by pedophiles, cars are used by bank robbers, guns are used by terrorists.
If you make illegal perfectly legitimate goods or services which have been misused by some, then pretty much everything would be illegal. As with most things privacy related, governments and law enforcement sticking their noses in to your business, building backdoors in to messaging apps, trying to ban encryption, tapping your phone lines, monitoring your internet history, or even banning mixers, does next to nothing to stop criminals and terrorists. It is a mass surveillance tool, nothing more.
I can't understand why anyone involved in bitcoin would be pushing for less privacy, not more.
There is a big difference with your examples. Cash is helping the society more legally, than illegally. Encryption is helping the way internet works more legally, than illegally. The internet is helping more innocent people than pedophiles and so on with the other examples.
But if mixers are used 90% for illegal purposes you have to see the thing a little more ethically no matter how much you like privacy.