Signing up for Coinbase isn't instant. Yes, you could find someone locally to exchange cash for Bitcoin, but that's hoping for a lot in terms of security, and isn't exactly convenient, either.
When I said signing up, I meant the whole process of getting to where you can actually exchange USD for Bitcoin. On Coinbase they ask for bank account information, and that can take several days to verify.
There is no process of identity verification on Circle before you can actually buy Bitcoin from them?
No there isn't. I have no idea how they pulled it off, but it really is instant. In less than 5 minutes, I went from not having a Circle account to having a Bitcoin transaction on the blockchain transferring BTC I bought with a credit card to my own private wallet.
The issue with this (as you probably know) has always been the danger of chargebacks.
I ran across a reddit post [1] discussing it. I dunno if they've completely dealt with the issue, but it is pretty fascinating to see they are even trying.
Of course it's not. But the argument of the parent poster was that you require a bank account. Also, most experienced traders on https://localbitcoins.com/ will prefer to meet in a very public place or in a police station, instead of an alleyway.
The parent's argument that a bank account is needed was a retort to the idea that Bitcoin is easier than banking.
Conducting financial transactions in a police station is not easier than using a bank, so whilst a bank account isn't strictly necessary it doesn't change the argument that Bitcoin is harder to use than regular banking.