It might be true if you are talking about market makers that have an advantage over other participants due to regulations. However nowadays market making on liquid instruments is almost equivalent to high frequency trading. The tail risk might be low if you have very low latency and perfect connection to the exchange. Anyway your pnl distribution will be negatively skewed. You are unlikely to lose tons of money like Knight (their testing algorithm kind of actively tried to do it) but making a steady profit is not easy in liquid markets.