Thing is, this is less about what we think about taint, and more about what the exchanges we are using think about it.
Just like banks, I believe they couldn't care less. All they care about is being compliant, so they can say "they tried their best". It doesn't really matter if the result is based on arbitrary criteria, and it doesn't matter that different exchanges use different criteria.
Banks don't care about AML, but they do about regulators fining and punishing them. So they are overzealous in reporting AML suspicious activities of their customers, sending loads of reports to the regulators.
No one will ever complain about a suspicious activity report leading to nothing, while dire consequences are for the banks that do not signal a real illegal activity. When in doubt, signal.
My experience with other regulated agents, like the one operating ATM in Europe, is that they tend to respect the bare minimum information required by regulators, but effectively reporting more than necessary in terms of transactions.