e-mail money transfers can be charged back.
Really? That sucks. I thought those would be fine since the money comes right out of your bank account.
People can claim to be "hacked", to complain that they did not authorize the spend. Since there is no signed paper contract, the bank will claw the spend back and leave the receiver with no avenue to arbitration.
You need to understand that thieves are attracted to liquid assets. Nothing is more liquid than cash. If you are trading out cash, you better be settled with nothing less than cash.
Services and continuing business relationships are served well enough by reversible spend vectors because those are items a thief cannot run off with. You can take a cheque from a stranger for a magazine subscription, but you better not sell laptops like that.
Nothing is more liquid than digital currency.