Do you truly believe that when you'd make the decision to categorize a transaction as such, that decision would hold up in court, beyond a reasonable doubt, every time?

If not, then you have no place making it. And I would argue that even if you do, you still have no place making it, as unaccountable private corporations should not be given the ability (or requirement) to enforce law.

Certainly we can legally require you to report suspicious transactions to law enforcement, but it should be up to people bound to follow due process to actually do something (or not do something) about it.

I think a reasonable compromise might be to allow payment processors to put a transaction on hold until it's reviewed by law enforcement, but even this has some significant downsides.