If the bad people are first using Conjoin, it would have been better for mixers integrity, than to be using mixers directly.
Nope. They'd then pull off one of their great psyops to convince you that mixers are bad regardless.
That will still be a good excuse than to be using mixers directly. I still think that mixers having AML check may significantly reduce the use of mixers by such group.
Mixers having AML checks would reduce the use of mixers by all groups equally, by approximately 100%.
As for implementing AML checks for mixers, that idea has one flaw. If the person mixing the coins does not have anonymity then why would they do it knowing there is a log that connects them directly back to the coins they want to anonymise?
Another flaw is that you're handing over your privacy for a privacy-enhancing service, while there are alternatives like coinjoin which don't require you to sacrifice anything. The AML mixer is a terrible business idea.