Bad trading is what causes the rapid price changes, not MM's. They don't care WHAT the price does, they get their commissions on buys AND sells. All they care about is that the stock remain liquid.
Remember, MM's are not TRADERS. They don't buy stocks to hold and sell at a profit. They buy when someone sells within their spread. They sell when someone buys within their spread. That's it. They are BROKERS, not TRADERS. they adjust their spread regularly. They all have different spreads. They compete against EACH OTHER not US.