Why should a handgun not be holstered with its hammer cocked?

The reason a handgun should not be holstered with its hammer cocked is primarily due to the increased risk of unintentional firing. When the hammer is cocked, the gun is in a state that is ready to fire with a lighter trigger pull, which can make it more susceptible to accidental discharge if the trigger is inadvertently pulled or if the firearm is bumped or jostled. This is particularly critical in dynamic or high-stress situations, such as during law enforcement activities, where maintaining control and safety is paramount. Keeping the hammer down provides an additional layer of safety by requiring a deliberate action to fire the weapon, thereby reducing the likelihood of an accidental discharge during the periods when the firearm is holstered.