Lucky you never having received a payment from tainted coins. People who used mixers in this forum either indirectly by being paid through signature campaigns or as a paying customer have in the past faced issues.
Tainted coins aren't just an issue when having to deal with state authorities, civil society often enforces filters voluntarily also. And if banknotes could be traced back so efficiently as bitcoin I'm sure many institutions would refuse transactions with them too.

There's no denying that traceability is a feature of bitcoin. That can be good or bad at times. But not that great for criminals who seem to meet their fate one one way or another with mixers. So no, the concept of "tainted coins" isn't a scam. It's a real thing. Ethics is also a thing and money doesn't always trump it either. I remember in this forum people used to get tagged as scamers if they accepted payment to promote ponzi schemes for instance. And well, by the notion that ponzi schemes are unethical, one might as well say the same for coins taken away from someone else via means of hacking etc. So when the traceability of BTC is used to catch criminals and seize their ill-gotten gains, we should consider it a great feature imo.