It's not unethical behaviour. It's simple business. No-one in any business is going to ask where their customers got their money from, you just try to make customers spend their cash on you rather than a competitor.
Banks have to comply with the law, of course, but beyond that you cannot expect them to hurt their business for no reason. This "holier than thou" attitude is hypocrisy, frankly.
Someone claimed that it was the bank's fault because they did nothing to prevent money laundering. Why would they if they are not forced to? When you run a business you do not turn customers away, especially they they want to give you plenty of cash... It's naive or hypocritical to claim otherwise.
None is blaming them for accepting funds from anyone that they come across, but there should be no confusion as to why the rules exist: because the banks will indiscriminately allow the transfer of funds from illegitimate sources.
With that in mind, the rules are crazy, because the banks don't care.
they must comply with the law and often they don't or they devise clever workarounds, abusing judicial loopholes, and sometimes they get caught and then sometimes some scape-goat might end up in jail for couple years.
until we see a mass execution^W^W real punishment of top management of all of large banks on this planet - nothing will change in the foreseeable future.
That is not an empirical fact. It's a specific interpretation of how things should be in the world. Some see it that way and other see it differently.