If you look back far enough, then according to centralized exchanges most bitcoin in circulation has been "tainted" in some way - be it from a casino or sportsbook, darknet market, scam, hack, DEX, mixer, coinjoin, or any of the dozens of other completely arbitrary reasons they decide a coin is tainted.
I have to admit that this reminded me of one conversation with a person who had a serious intention to invest in Bitcoin about 3 years ago, but after several months of research it was precisely this issue that emerged as crucial. One simply wondered for a reason whether it could happen that the BTC he buys would be marked as tainted in the future and that in that way he would be left without everything. The only thing I could say then (and to be absolutely sure that this would not happen) was the advice to buy BTC directly from the miners.
If we go far enough in to the future, then every bitcoin in circulation will be tainted in such a way.
It may be the curse of any currency, because it is used by good and bad people, and perhaps the best argument to fight against being abused with the argument
"you have tainted coins" is to stick to the proven fact that most banknotes are contaminated with countless illegal activities, and yet no one checks them when we pay with them.
We should not be accepting these arbitrary rules and limitations which exchanges are dictating to us.
Of course, we should not accept every nonsense that they try to impose (exchanges), but I think that they do not do such things because they want to, but because the law increasingly forces them to play detectives and look for anything suspicious. The problem is that they want to know everything, and when (if) they become more aggressive, users may start using DEX more.