Should forum admin consider to stop all campaigns related to mixers?
Just stop if it's the last solution. But I don't think forum are going to stop it just because mixer services provide an opportunity for anyone to increase privacy. Abuse of the service should be excluded even if some people use the mixer to obfuscate their bitcoin transactions for prohibited things, the conditions should be the same as when bestmixer was confiscated. This means that the forum doesn't stop advertising other mixers.
So far I haven't gotten any red flags about the existence of a mixer on bitcointalk especially to anyone using it legally.
The FBI and other law enforcement agencies are still carrying out investigation therefore it will be too early to conclude the Chipmixer issue. Every product or service can be abused. It is not wise to just stop mixers advertisement because other users in countries outside of the US are not affected by this findings or investigation. The forum is an international platform that is not governed by the laws of any country that is why it might not stop the advertisement of mixers. Mixers are not generally bad but the wrong application of this service is what is giving this service a bad name.