And it's not a few coke dealers, it's tens (hundreds?) of billions in illicit money being laundered by the major banks.

If it were voluntarily you could continue with the transaction if the two private parties were OK with going forward without KYC. The analogy here is when stopped by a policeman and asked to search, you can decline and continue walking on with your voluntary activity -- if the policeman told you that you had to turn around and stop your voluntary activity for declining the search then it would violate the 4th amendment and the search would be involuntary. In this case the voluntary activity is engaging in services that involve government-imposed KYC.