A lot of bacteria grows in the range of 40-100°F (4-38°C) (i.e. room temperature). It's definitely not recommended to defrost meat at room temperature. In fact, you are not supposed to leave meat at room temperature for more than an hour.
However, defrosting in the refrigerator can take a long time and require you to plan at least one day ahead of time. which leads to a safe and fast solution: Defrost meat in a waterproof ziploc bag in cold water. Change the water every 30 minutes until defrosted. The water is a better conductor of heat than air, so the defrosting is quite fast and the water is cold so there's minimal safety risk.
