Getting weekly fat pay checks from mixers clouded some users judgement. I noticed that too but me being right wasn't going to change anything so I didn't say it too often (I think i did it once or twice at least though) and I didn't have to. It would only upset the people who were carrying the mixer signatures even more.
Those mixing services were centralized and nobody knew what data they were logging. It could be anything. As far as I know none of them were open source even if they were, it still wouldn't make any sense to use them because you still wouldn't know the actual code they were running on their servers. To function, they needed other people's coins so them being open source wouldn't make any difference.
Even the mixers that moved to the altcoin forum, some of them turned out to be a scam and some of them disappeared without any notice. There have been some very obvious red flags with some of these mixers but due to users’ sensitivities it has been a subject that is almost impossible to discuss in good faith. Even the mildest criticism is enough to get people enraged and making accusations against you.
Even governments and banks can go bankrupt or scam you, so it's no surprise that some mixer services are scams. Everything is run by people and for business purposes so anything can happen.
I am not for or against bitcoin mixers but we cannot claim that all are scams or not worth using just because some projects are scams, there are still reputable projects.
But I agree with you, mixer topics are difficult to discuss in a friendly and fair manner, we are vulnerable to attack if we express opposing views to those who are wearing the signature of a mixer signature campaign. That is understandable because their income is generated from there and they would not be comfortable if their source of income was threatened. If we were in their shoes, we would do the same.