Bitcoin mixers and coin mixers in general are only designed for criminals and are only used for criminals.
The argument actually goes the other way round:mixing in general is mainly a necessity because e.g. exchanges are complicit in the criminal act of "chainalysis" which is pretty obviously contrary to the privacy rights of e.g. European citizens.
Mixing is the only defense against the criminal act of chainalysis.
The legality of chainalysis is probably highly dependent upon your local jurisdiction, but as a European citizen, European law applies to my personal actions and also to the actions of foreign actors against me.
Which is why chainalysis that affects me is a crime.
And in fact, all chainalysis affects me.
Defending against a crime is not a crime in and of itself.
Even acts that may be considered criminal under different circumstances lose their status of illegality once they are committed in self-defense.
E.g. the use of lethal violence against another natural person is usually a crime.
In self-defense, it is not.
Therefore, for the approximately 450 Million EU citizens, mixing is not a crime, because chainalysis is in fact done against every single transaction on the Bitcoin network at any given point in time, which makes every single European Bitcoin user the victim of a criminal act, against which defense is legal.
For a European, mixing is most likely not only not a crime, it's a duty.
Defense against foreign criminal acts committed against the total of all Europeans is the legal basis for things like universal conscription, military expenses etc. pp.
In other words: Fellow European, I want you to mix your coins!
When chain analysis would be illegal then those companies won't exists. Simple as that.
And its not in any aspect self defense to mix his coins to protect oneself from a crime. The comparison with deadly self defense is very bad.
And basically nobody cares what you personally think is illegal or not
Prisons also don't care because a drug lord think his threaten illegally because he has only 3 programs on his tv.
So you want to protect every criminal because everyone has his own little reasons. So we should run criminals away with millions in bags because they think it would be illegal to search their bag.