Whether you fund UBI through printing or not is unrelated to the function of banks. Society still needs to divert extra cash to people who are extra productive with ideas and businesses. But how do you know how much extra money to give to whom? You make a dedicated layer in society who's sole function and incentive structure is to distribute that money to those most likely to use it best and name it "banks".
I'm with you. Eventually people would probably create something like banks from their pooled M0 created by fiat. But unlike the current system everyone would be aware it was their money and not some intrinsic value of the banks' so there'd be significantly less nepotism, corruption, etc. Just the initial sheer distributed nature of it would significantly help.
Those extra productive ideas and businesses generally aren't. It's just that money begets money and then people confuse being wealthy with positive traits enabled by having money, like productivity.
