The purpose of a safety is to make the gun not go off if you drop it. The original full name is “drop safety”. The easiest way to do that is to have a switch that makes it impossible for the hammer to fall, the firing pin to hit the primer, or whatever and keep the switch on when you aren’t shooting. That way if you drop the gun it can’t go off.

Guns “without a safety” still actually have a safety. It’s just automatic in some way, so you don’t have to use a switch. Usually it’s something that blocks the striker or hammer from falling until the trigger is partially pulled.

This is why if a gun has a manual safety, you should use it, even when modern practice is that handguns shouldn’t have a manual safety. It’s not a modern doctrine changed because reasons, it’s the way that firearms function mechanically has changed, and the doctrine changed to match that.