This is really putting me on the spot.
There is no argument: 98% of things clear overnight. It was left in Bill C-8 as the one barrier the banks could still have in place that would mean that nobody with a low income, no one on social assistance, would open a bank account. It was a loophole left, on purpose, to give the banks an excuse to say that doing so was legal. All the other means that the banks were using for turning people with low incomes away--you have to be employed, you have to have a minimum balance in your account at all times, you have to produce five, six, seven pieces of ID--were made illegal under Bill C-8.
This one was left so the banks could continue to facilitate, as the federal government has, the growth of a two-tier banking system, in which the banks don't want to deal with people unless they have money, something to invest. Everybody else can go to the cheque-cashing outlet and get gouged even worse than they would at the bank. This loophole was left open so the banks could still turn people away.