We are already on digital age or era which means that anything that do implies nor involved with anonymity will surely be considered to be one of the best ways on making out these illegal transaction.
Those words you have said was indeed true somehow but there are other coins which is more anonymous that Bitcoin itself which is im talking with Monero etc.
It is just a wrong perception to have this to be implied on mixers because they arent really created solely for criminals but rather on pure anonymity itself.
They are just taking advantage with that one.