I think the use of the phrase "don't trust" is not really appropriate in this context. I would certainly "trust" a Glock to go bang every time the trigger is depressed, whether intentionally or unintentionally. The question is whether you
want a switch/lever on the gun that toggles the gun between "safe" (as safe as a loaded gun can ever be, anyway) and "ready to fire." I think it is fairly self-evident that having an additional step that must be taken before the gun will go off will reduce the number of AD's/ND's.
Without some operator error, you won't have an AD/ND in a non-defective Glock. But there has never yet been a system with human input that does not have an error rate. Never. Doctors go to school for years to learn how to safely and effectively care for patients. But sometimes mistakes are made. That's why hospitals try to implement procedures that are backstops against mistakes. The same is true for professional pilots. They are generally highly-competent, highly-trained individuals... far more so than 99% of civilian handgun owners. But they have procedures, mechanical systems, electronic systems, and other mechanisms designed to overcome the occassional (and inevitable) errors, and to require
multiple errors before an accident occurs.
So, the question is, do you want one additional layer of safety before an error becomes an accident? Everyone has to make up their own mind, but I'll take the extra layer. I'm very safety-conscious, but I'm a human being. Even though I've personally never made a mistake yet
, the data from the rest of humanity says I am likely to make one sometime. If that occassion happens to be while I'm handling a gun, I'd like to have to make
several mistakes for that error to be the worst moment of my life.