There has been a long debate about whether speculators are stabilizing or not. We consider a model where speculators have a stabilizing role in normal times, but may also provoke large risk panics. The very feature that makes arbitrageurs liquidity providers in normal times, namely their tolerance of risk, enables a large increase in asset price risk during a financial panic. We show that a policy that discourages balance sheet risk reduces the magnitude of financial panics, as well as asset price risk in both normal and panic states.