That’s why generally speaking you don’t launder money by just soliciting input, shuffling some bits around, and then providing output.

You launder money by operating a tangential legitimate enterprise. So, to pick the humorous example: you open a laundromat called Bill’s Cleaning, and then ostensibly you have expenses and profits related to laundering clothes, but you pad your books with fake wash/dry cycles to cover your illicit in/out flows.

You are essentially correct.

Many (if not all) blockchain analysis companies give a higher risk score to coins that have come from a mixer aka they are "dirty".

I don't just mean practically. I mean legally.

Cryptocurrency advocates often ignore this. They think they are solving bureaucracy with math. They think that whatever they can do technically with smart contracts and money transfers is legal. They think they found a loophole in AML and KYC laws. They have not.

It's the old ignorance of "I'm a good engineer, so the legal issues must be a minor detail I can just solve with code".

They seem to think that the legal roadblocks were put in place by accident of history. But no, they are actually codifying almost entirely society's intention. Perfectly? No. But infinitely better than what cryptocurrencies are trying to do.

To spend it on illegal things.

Right. I agree that it naturally follows that the only two reasons to use mixers is if:

1. You have committed a crime (dirty money) 2. You are about to commit a crime (buy illegal stuff)

Sometimes both.

In other words, like I said "Only a fool would use a mixer for legitimate purposes".