Adding this sort of friction would increase spreads. Market makers are a net positive for markets (who buys/sells when no one else wants to?), and I don't see a

Adding this sort of friction would increase spreads. Market makers are a net positive for markets (who buys/sells when no one else wants to?), and I don't see any downside to allowing them to manage risk and trade quickly. I think the way to increase fairness is to change the way orders are matched.