If a person or firm has a reasonable belief that a business partner is committing crimes or even just behaving unethically, I would say they have an obligation to curb the activity or end the business relationship.
This idea that only the courts should limit or punish crimes pops up here once in a while and I've always found it bizarre.
If child porn was not a crime would you be ok with Visa and MasterCard doing something then? Is it in your view that should they only not do something because it's a crime?