So S&C get a huge fine for having traded with Iran. Naughty boys. In our capitalist society, nobody will question that banks are there to make money, which by definition is odourless. Punishing a bank for dealing with X is morally identical to punishing Smith and Wesson when a gun they manufactured is used to kill X. If a criminal steals a gold ingot and buries it, are you going to take the soil to court? Going after banks is no more than a short-cut to apprehending the criminal in the first place. Much easier of course, but fundamentally incorrect.
Lest I be misunderstood, I have not the least sympathy for bankers and their ilk, but “money-laundering” is a euphemism for “finding the criminal is too much effort”; there’s nothing wrong with looking after X’s money; if X got it illegally, then have him punished for his crime. Smith and Wesson anybody?