The purpose of a bitcoin mixer is literally to hide the source of funds, which in any other financial transaction would be classed as laundering.
So all cash transactions are classed as laundering? Don't be ridiculous.
Anyone who owns these sites know full well that the majority of their customers will be sending dirty money through their system in order to try and clean it.
Absolutely not true. Only around 8% of coins sent to mixers are what you might term "dirty money". The vast majority of funds come directly from KYCed accounts on centralized exchanges from average users simply seeking to reclaim some privacy. Source:
https://cointelegraph.com/news/only-8-of-mixed-crypto-coins-tied-to-illicit-activity-reportThe feds also get to seize large sums of money and also figure out lots of customers who might have been trying to avoid taxes - people should stay far away from such services or they might get a knock at the door in future.
If you've completed KYC on a centralized exchange, then your details have already been passed to your government. It's KYC you must avoid if you don't want the government knocking on your door, not mixers.