How are random people displaying advertisements of mixers in exchange for some Bitcoins = scammers?
Because there's no service at all, a "mixing site" is just someone else's Bitcoin wallet. By using someone else's wallet to aggregate the stolen money, the scammers who are paid to spread the deposit link can keep repeating the process of stealing without ever getting banned:
It doesn't matter if they "couldn't have known" that Chipmixer would scam everyone, it matters that they "could've guessed" it would. After the Chipmixer scam, its promoters immediately switched to promoting the next scamming site. And after that mixing site scam predictably took everyone's money, guess what? These same promoters would move on to post ANOTHER mixing site scam in their signature.
These scammers understand a mixing site is just someone else's Bitcoin wallet. This allows forum users participating in these signature promotions to scam over and over and over again by just blaming their boss for taking all the money (while they get paid their cut of the scam up front for helping spread the scam's deposit link across the forum).
If we're talking about ChipMixer, did they actually scam? Or did some government entities merely didn't spprove of their service?

I'm very confident to say that the participants of their signature campaign don't know or never had knowledge of the internal operations of the mixing service. They merely want to be incentivized in Bitcoin by joining the campaign.
Plus about "aggregation of stolen money", entities could also do that through JoinMarket and through those coordinators, no? It merely preserves Bitcoins's fungibility if you ask me. Crime doesn't exist in the blockchain. The coins are coins.