Forcing banks to absorb the losses of this write-off will likely make it harder for the poorest to access credit in the future. Banks are not social institutions - they're pathological profit making entities. They will have no qualms with raising interest rates or denying credit altogether to compensate for the increased risk of doing business with their poorest customers.
The poorest section of the population do not borrow money for no reason. Borrowing is often required for emergencies (i.e. medical) or short term liquidity (paying bills on time). Just as importantly, it's vital for people who want to improve their economic situation by starting new businesses.
My primary concern is that banks starting to shut/price them out. The least well off will end up resorting to informal lenders (i.e. loan sharks).