Yes, I get the desire for a pound of flesh, but a tax on deposits, especially when you are saying this one-time thing won't stop countries and banks from running up debt. If the subtext is that this is the only time we are going to ask for deposits, what's going to happen the next time - we put that country's youth into slavery. It's not believable. That's the problem with selling one-offs.
Seems a little extreme. The last proposal was to tax small accounts just 3%.
A tax focused on bank accounts and not general wealth or income will have a strange incidence, and seems extremely unfair. And no matter how small, it can do a lot of damage to the banking system. Whenever you impose a tax on deposits you push people to find alternatives. And that means more money ends up in the shadow banking system, which is much harder to regulate. That's what in part led to the U.S. financial crisis.