Nobody is going to pay $20 to process a transaction to buy groceries.

Expanding on this a bit there are several solutions to this problem.
First off, there is some margin available because credit cards charge merchants 1.5%-3.5%.
So every $1000 spent today is already a $15-$35 fee.
I would personally have no issue building a credit line with Amazon by sending large chunks at a time rather than on every single purchase. This doesn't work for everyone else living paycheck to paycheck.

There's also the ability to borrow against the Bitcoin which is probably the best option.
Never sell the BTC and just borrow thousands against it.
But again maxis reject the idea because they assume eventually there will be nothing else to borrow and everything will be Bitcoin. So yeah it just reaches absurdity at a certain point.