Mechanically, Glocks are no less safe than any other quality firearm. However, they are reasonably unforgiving of mistakes. The relatively light and short trigger movement before the loud noise doesn't provide as much warning as some other systems, such as a DA/SA auto. If you put your finger on the trigger under stress, reholstering, etc, it will go bang, just like a DA/SA that hasn't been decocked.
Most NDs I'm personally aware of came from a deliberate trigger pull. The mistakes were thinking the gun was unloaded and more than one came from reversing the unloading sequence (cycle slide then drop the mag).
I've seen, and investigated, NDs from just about every common law enforcement weapon system ranging from DA revolvers to ARs. It was never the fault of the weapon, always the user.
Ken