What makes you believe that? The overwhelming majority of savings are held in bonds, stocks and real estate, not in paper notes in a vault. You might quible over the usefulness of savings and investments vs other allocations, but assuming is useless is pretty extreme.
That is why banks are not evil. On the contrary: they are the basis of a healthy economy.
OTOH, it might be debated that banks which take your money leverage it out and get huge returns while giving you a fraction of a percent, banks that charge 2-4% transaction fees for basic transfers for merchants, or fee harvesting people for more than their net worth are more economic parasites than useful service providers.
Much of modern banking in countries like the US are basically shifting wealth from the economic value creators to a few vampires growing their own personal fortunes which dwarf that of the other 99.999% of the population. The idea that they might return some of that to their customers though interest bearing checking accounts, removing low balance fees or any of their other abusive practices never comes up.
And precisely because banking is so essential to economy, its corruption is one of the worst events in an economy.
I haven't fully thought this through so please poke holes in the argument if you can :)