There will always be people who don't want their funds traced, or for whatever reason will insist on using cash.
There is so much data already collected on (and information extracted from) debit/credit purchase records and money transfer records and grocery store club cards and everything else we sign up for... sometimes it's nice to be annonymous when you're buying an ice cream cone and not sticking to Atkins....
Do we really want the "Minority Report" targeted ads? We're getting close, as it is.
I used to have a customer (non-account holder) who would grudgingly come in to buy money orders for things he absolutely could not pay cash for -- and he paid for them in silver dollars. He didn't even trust paper currency.
We have an employee here whose fiancee won't keep their funds in a bank account, they keep cash in a safe at home. Kinda strange, but there it is.
People want their privacy. Some more than others, but the desire will always be there.