Pretty much every law enforcement agency carry Glocks, which don’t have a manual safety.

As I understand it safeties on auto-loading pistols were developed to stop the gun from firing when dropped, so that they’re as safe to carry as a revolver.

Also seriously don’t trust any gun to be safe, ever, seriously.

Yes. When you’re not using it or not expecting to use it the gun safety is on. You also train an absurd amount of the time practicing with your firearm and instinctively drilling the flick of the safety on/off into muscle memory whenever you are going to use the firearm for its intended purpose.

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.