Of course there are tainted coins. Try spending known Silk Road coins for instance.
The article you linked is from 2019, and the CEX in question is just playing a good guy, while at the same time they avoid doing business according to the rules and profit in billions without paying taxes. Most of the BTC that were seized from Silk Road were sold at auctions and, lo and behold, they are no longer taint because they were laundered by an agency with three letters
How do you guys promoting mixer coins spend your BTC? When the taxman asks for origin of the money I guess they wouldn't enjoy you promoted a mixing service, specially if you made money from ChipMixer which was closed, so not sure about that. I would be paranoid for instance, to spend ChipMixer related coins with Bitrefill or even put them on an exchange. And if nothing happens who knows in X years you end up in trouble. This is the problem with BTC, its not fungible. As far as I know, promoting on sig campaigns is legal since it's just marketing, but not sure when the promotion is a mixer. I wonder how people are using their money there. From what I've seen they do nothing with it but hoard it. As far as P2P, I don't trust people in real life, you never know who you are meeting with, and Bisq doesn't solve anything as far as fiat transactions, you are risking it the moment you do a bank wire.
I've never had a problem with a transaction being rejected/frozen regardless of the fact that the coins were mixed, but I don't use CEX because I think they are more negative than positive overall. There are many ways to achieve privacy when it comes to the BTC you have in your wallet, but some things are not desirable to discuss publicly.
If you are worried about things like taxes, you think that someone is constantly following you, eavesdropping or something similar or you are too paranoid, then maybe Bitcoin is not for you, considering that you are turning a solution into a problem.