I’m honestly having a hard time figuring out if you are just really naive or perhaps mentally challenged or if you work for a bank. Please tell me how well banning drugs, prostitution, and guns, and ANYTHING else that people want to do or use has gone for ANY government anywhere… All it does is making it more expensive and more profitable for a fewer number of people.
Worse, now you are proposing to ban a decentralized item. It will laugh in your face.

You entire argument is “We do a poor job of securing our networks, therefore we must use the violence of the state [ineffectually] to stop it”. The correct answer is “we must do a better job of securing our networks”. Its not impossible. But it requires paying people who are good at their jobs. Companies should feel the real costs of their oeprations. When you ban things you hide the actual costs of doing this, and further make side effects exagerated. Why would someone who is doing something illegal, stop doing it, just because you made something else illegal?

Frankly, it’s a moronic proposition.