That might make sense if the bank wasn't also acting as an agent for the government, with potentially severe, life-changing consequences if they hear something they don't like.

If the question was purely for my protection, then I could simply answer "I don't wish to share that information."

But I can't actually answer like that, because it's too risky.

There's also no option to opt out of such investigations. I didn't request the bank to protect me from my own actions. When there's a credit card transaction that they suspect is fraudulent, they ask "did you authorize that transaction?" That's fine, and that's all they need to know. Asking me who I'm paying and why, with implied duress, is a completely unwarranted violation of my privacy.

There's also a serious issue with an assumption of guilt in these cases. Look at the case of Donald Trump right now, suing Capital One because they closed over 300 Trump business accounts due to suspected money laundering. In Trump's case, I can well believe that there was some kind of corruption, money laundering, or other criminal activity going on. The man is a documented criminal. But the bank is making a decision to penalize someone, potentially severely, without any meaningful due process. Guilty until proven innocent. For someone without the resources Trump has to challenge something like that, what chance do they have of getting a fair outcome?

This is all completely unacceptable in a supposedly civilized society, and you should not be defending it.