It is a matter of principle.
It just doesn't make sense and I don't see why I should carry that burden.
There are many reasons your allegory doesn't apply - 'people who want to pay cash' are not a protected class. Serving people with disabilities doesn't put me at risk of theft either, nor does it increase my banking costs.
You're going to have to show some pretty good evidence of a positive social outcome to make this persuasive, because it is adding a big burden to business. (And unbanked figures in the US are not that - US society is very backward in its attitudes to banking and payments, and in giving access to banking to everyone)
The argument that is being made is that people who want to pay cash should be a protected class, with their ability to transact protected in law, so that every participant in society may benefit from those rights should they ever be needed.
I'm not seeing it here.
ironic