Once you start claiming "malfunctions or internal damage/unauthorized modifications/breakage." then any/all examples/scenarios you can give is a moot point as this applies to the other safeties as well. Further discussion using this method is simply debating for the sake of debating.
I'm not sure what you mean by this.
It is not a matter of opinion that the firing pin safety can, and is intended to, prevent discharges from events that the drop safety can not prevent, it is a fact. A single example is sufficient to prove this, but I will provide more than one.
If the firing pin lug breaks, the trigger bar/sear can no longer prevent it the firing pin from moving forward even if the drop safety is fully functional. In that event, the firing pin safety can and will prevent the discharge.
If the trigger bar is damaged or modified so that sear engagement is insufficient, then the trigger bar can release the firing pin to move forward even if the drop safety is fully functional. In that event, the firing pin safety can and will prevent the discharge.
If the frame of the gun is damaged or warped, this can result in improper tolerances and interactions between the frame parts (trigger bar/sear) and the slide parts (firing pin) resulting in the firing pin not being properly engaged by the sear. In that case, the drop safety will have no effect but the firing pin safety can and will prevent the discharge.
If the slide separates from the frame (slide rail breakage or other catastrophic failure), the trigger bar/sear (and any other frame parts) will come out of engagement with the slide parts. In that case, the drop safety will have no effect even if it is fully functional, but the firing pin safety can and will prevent discharge.
Basically, the drop safety prevents the rear of the trigger bar from being manipulated downward (which will only be beneficial if sear engagement is correct and the sear and firing pin are relatively intact) while the firing pin safety actually blocks the front of the firing pin even if the slide is removed from the pistol.
In other words, not only does the firing pin safety prevent discharges the drop safety can not, it also works in a very different way--it directly blocks the firing pin from the front as opposed to merely restricting the horizontal motion of the rear of the trigger bar.
Since that is, without a doubt and beyond any reasonable debate a true statement, it is absolutely incorrect to state that the firing pin safety does nothing other than act as a backup to the drop safety. Clearly it does things that the drop safety can not do and therefore it is more than a backup to the drop safety.
As far as discussing "malfunctions or internal damage/unauthorized modifications/breakage" being moot, I don't understand how anyone could arrive at such a conclusion unless they were laboring under the misapprehension that such issues never occur or that they are not important to firearm designers. They certainly do occur and are most definitely a consideration in the design and testing of passive safeties.
Trying to avoid them in a discussion of the intended function and importance of firearm safety features makes no sense at all.
The only possible reason I can see for your attempting to exclude them from this discussion is that their existence and the design steps taken to neutralize them severely hamper your ability to defend several of your assertions. There is certainly no logical or realistic basis for their exclusion from the discussion.
Similarly one can also claim that the manual safety "performs functions that the trigger safety can not perform".
That may be correct, however, I was, as I explicitly stated, relying exclusively on your statement that the manual safety simply locked the trigger bar in place. If your statement is not correct, then it may be true that the manual safety performs functions that the trigger safety can not.
So by this, you obviously rank the Magazine safety as well as the manual thumb safety behind the standard 3 "Glock-like" safeties.
To be accurate, I simply hadn't considered magazine safeties at all. So far, I don't have any firearm applications that call for magazine safeties.
As far as the thumb safety goes, its value depends on the design of the rest of the system in conjunction with how the gun is to be carried. A properly designed passive safety system (like the one Glock employs) does not require a thumb safety unless the user chooses to carry the gun either unholstered, or in a holster that does not adequately protect the trigger. Then the thumb safety is important because the system is compromised (at least to some extent) by the failure to adequately prevent the trigger from being inadvertently operated.
The other consideration with a thumb safety (or any manual safety) is that its presence incurs a training penalty on the shooter. Because of the possibility of it's being inadvertently activated, it can not be ignored. The user must include the deactivation of the safety as part of the shooting drill to insure that it is always deactivated as a matter of course during the normal presentation of the pistol.
