You should be able to achieve this without also enabling terrorism, child pornography and extortion. Because of this Tornado Cash was never the right solution - it requires you to permit these things just in order to have privacy. In other words it is a bullshit technology and deserves to be replaced with something better. If blockchain in turn requires a solution like Tornado Cash in order to offer any privacy, mandatorily fused with the aforementioned radioactive side effects, then blockchain itself is a bullshit technology.
Just because you find a use for a technology doesn't make the technology good. Nuclear weapons are a highly effective alternative to insect repellent, but that does not justify the general purpose use of nuclear weapons for repelling insects.
The problem with this line of reasoning is that any general purpose technology can be used for all those evil things. Hell, should we sanction the Linux kernel project, because all of those nasty people use it?
If Linux were a focal point for enabling North Korea and Iran to develop nuclear weapons, then yes, sanction the hell out of it. But sanctioning Linux would have such dramatically negative societal effects that it would outweigh any benefit - the same is not true of a mixer. Mixers in my view have absolutely no legitimate use, their exclusive purpose is the enablement of deviant behaviour in one form or another free of societal accountability, and it'd be a red flag for me just to know someone used one regardless of knowing why they used it.
It's like saying the local brothel can't be shut down because the building could potentially be used to teach the word of the lord while the employees aren't otherwise busy. The exclusive purpose of the brothel's existence is enabling trafficking and sex work, and the benefit of any potential imaginary supplementary uses are grossly outweighed by the benefit to society of closing it down.
I agree, I feel this is a bad line of argumentation. If we take it a little further it's clear that the human brain can be used for extortion, money laundering and cybercrime - and therefore it should also be placed in the same sanctionable category as all the nasty people use it.
I love how you blew through my reply from 15 minutes earlier clarifying the obvious concept of the balance of societal benefit to post a me too comment. Do better
Just because you find a use for a technology doesn't make the technology good. Nuclear weapons are a highly effective alternative to insect repellent, but that does not justify the general purpose use of nuclear weapons for repelling insects.