Bitcoin is for everyone so are Bitcoin mixers and cryptocurrency mixers (altcoin mixers).

Criminals can use Bitcoin blockchain, Bitcoin mixers, altcoin mixers and it's not responsibility of mixers. It's very old story, like if a criminal used a knife, a gun to kill someone, he must be arrested and be responsible for that action. The knife, gun producers and sellers are not responsible for the criminal action.

Same with Bitcoin, altcoin mixers but treatment against mixers are different because of anti-policies from governments. That's it practically but it doesn't change fundamentals of mixers.