For example: https://www.reddit.com/r/Banking/comments/1csl00q/any_banks_...
Zero. Because FINCEN/KYC[0] laws in the US mandate identification for all customers.
Which means that at least 3% of the populations is "unbanked"[1]:
Some reasons a person might not have a bank account
include:
Lack of access via a nearby bank branch or mobile phone
Minimum balance fees
Distrust of the banking system, typically due to lack of transparency
regarding fees and deposit timing[1]
No access to government-issued ID, which is required to open a bank account
To avoid delinquent debts, such as creditors seizing the account in
judgements, or the government collecting back taxes or child support
[1] https://en.wikipedia.org/wiki/Unbanked
Edit: Fixed subject/verb agreement (laws/mandate)/fixed quote formatting.
https://www.bankhelp.gov/help-topics/bank-accounts/required-...
Add on top of that undocumented people or the issues surrounding the Native American population and their partial autonomy rights, and it becomes a mess very very quickly because it won't stay at "about three percent".
And then they have someone with an incomprehensible accent in a call center that probably also runs scam calls calling you up and asking for your password as part of their ordinary SOP.
They deploy fancy new tech like "verifying your voice" with some AI crap while simultaneously not allowing your password to have more than 8 characters. (Which must have two symbols but if one of them is ` you'll experience random spontaneous logouts).
There may be many causes of the disaster that is bank security, people not having ID is absolutely not part of it.
The problem isn't the banks, the problem is that unlike Europe where in most countries it's commonplace for everyone to have a government-issued ID document, the US does not have that requirement and so companies of all sorts abuse documents not meant for that purpose like SSNs or driver licenses that can be trivially forged.
Banks can't invent security out of thin air when a significant part of the US population believes that mandating possession of one is a surefire way into a dictatorship or whatnot.