The unhappy theory of business ethics is this: you have a fiduciary responsibility to maximize profit. Period. To do anything other than that is to cheat your investors. And in a competitive world, you don't have much wiggle room here.
And so it can be very much in the interest of bank A to sell-short bank B shares, or buy CDSes on bank B, because they have exposure to bank B. It's the responsible thing to do as a fiduciary, and yet if everyone does it at the same time, it's destabilizing because everyone is selling.
What is needed for a sound expansion of production is additional capital goods, not money or fiduciary media. The credit expansion is built on the sands of banknotes and deposits. It must collapse.