There's always a way to make sure a gun doesn't go off when the trigger is pulled. Unload it, put it in a locked case, then put that case in a safe. If you treat a Glock this way they are most always safe.
I don't know what else to say. They function as double action revolvers with semi auto properties. No safety there either. Some folks will never accept them. But as I said, if there were LIABILITY or SAFETY issues, no police agency would use them. There aren't, and they do.
I agree that police departments would not deploy Glock pistols as widely as they do if they were inherently unsafe.
I don't know precisely what firearms training police officers undergo before being turned loose on the job, but, just from what I've overheard at the range, it sounds like they receive extensive training and must qualify before they are ready for the field.
Now lets examine the minimum qualifications for lawfully owning and carrying a Glock, or any other handgun, just like a trained police officer does, in Washington State, lets name him Jon Doe and assume he's never owned or handled a handgun:
Jon must be an adult and a resident of WA.
He must have a clean, or laundered, criminal record.
He needs to have about $600 to buy the gun, holster and ammo.
He needs exactly 5 days of patience while the background check clears.
So, there is a chasm of Grand Canyon proportions between these two individuals when it comes to firearms proficiency.
Whereas an additional safety on a service pistol may be a hindrance or even a life-loser for a policeman, it may also be the one thing that keeps Jon Doe out of trouble, assuming he's smart enough to use it.
And of course, this is not an either-or scenario, it's a continuum, heck, some members here may even be better trained and more proficient than police officers.