Why does Square Cash require my social security number?

Episode 1430 (1:06:43)

George from Aurora, IL
Venmo

George wanted to use Square Cash to send friends cash, but it requires his social security number. That's not a great idea and Leo says to refuse giving that out everywhere. Technically, they're not supposed to ask for that, but everyone does. So he should just say no. Leo suggests Venmo. There's also Cash.me. Banks use Zelle. Leo wishes that pay services would just go open crypto, like BitCoin does. You keep the private key, but give away the public key.