If private parties come to believe in the possibility of policy actions that will relieve them of some of the costs of poor decisions or even just bad luck, their incentives to appropriately weigh risks in the future will be reduced and discipline on managers watered down. Weaker market discipline distorts resource allocation and can sow the seeds of a future crisis.
The possible real costs of policy actions implies that they should be taken only after the determination that, in their absence, the risk is too high that the crisis will disrupt the real economy.