Why is it unsafe to marinate foods at room temperature? Doesn't the acid in the marinade kill any bacteria that might be present?

Bacteria grow rapidly at room temperature, so for food safety purposes, food should always be refrigerated while marinating. (Refrigeration slows bacterial growth.) Marinade that has been used on raw meat, poultry, and seafood contains raw juices. These juices may contain bacteria that, if eaten, could make you sick. The acid in marinade doesn't kill bacteria, it merely slows or stops bacterial growth.