These "safety" features make guns less deadly, in the sense that they make guns less reliable in the first place. If you're using one to defend yourself, your family, or your home, that might actually make the gun less safe in the sense that it won't work when you need it. This defeats the entire purpose of having a gun.

Guns also have safety features that protect against accidental discharge, namely the trigger safety. Some guns have an additional trigger safety that triggers if the gun is pressed against something (or someone). Since these features don't reduce the reliability of a gun when it is intended to be used, the NRA doesn't have any problem with them, and at least the trigger safety is standard on all guns.

The NRA also does a lot of work to teach firearms safety to children (which basically boils down to "don't touch it and tell an adult if you find an unexpected gun somewhere"). For those who do shoot, the NRA is also good with basic safety principles.