The thing with mixers is they only had one use: that is to disguise funds by taking them from once source and "cleaning" them by paying out from a different source. That is the very definition of money laundering, which is why they were chased and shut down by every financial regulator who could find them. They might have come up with other claims, such as trying to keep the anonymity of Bitcoin, but they earned fees from every transaction so it was in their interest to keep them up as much as possible. Casinos like you say, have much more stringent anti money laundering controls because they were historical such a big avenue for criminals to wash their money and now the authorities know all the tricks, so they are generally more respectable.