I lot of it does have to do with what a person feels comfortable and confident with. To not trust yourself to safely lower the hammer on a semi, wheelgun or lever gun, etc. speaks a good deal about the lack of training or sense of competence with mechanical devices.
[Gloob]
I absolutely trust myself to manually decock certain guns. But trying to keep a hammer from slipping is one thing I'll never trust myself with.
You may have misinterpreted this statement. Unless you are suggesting that when decocking a 1911, the only thing between a successful decock and an ND is your thumb on the back of the hammer spur. If this is the case, then you have read me correctly, and I will forever maintain that no matter how coordinated and dextrous you are, this is not a safe practice. Read the ND thread. Every one of those "hammer slipped" NDs was by someone who had done it hundreds of times and felt completely confident. It's just not worth the consequences, even if you have it pointed in a safe place, unless you are already deaf. On the range, with hearing protection, pointed downrange where the rest of the bullets are going, yeah. In your home, no ears, after loading your gun, no. Especially if you are within city limits where such an ND could constitute an illegal discharge of a firearm. Or you have neighbors/family/friends/coworkers/employers that would find out and forever have a doubt in their minds about your competence and safety.
It's the people who ARE (improperly) "trained" and confident enough to be comfortable decocking a gun in an unsafe manner who are the ones that have NDs. If you are competent enough to know how a modern gun fires and the safety mechanisms it has built in, you would NOT rely on holding the hammer back, alone. There is a much better and more fail-safe way to decock most modern handguns, period.
Besides, like I said. What firearm instructor teaches decocking? Where does one get this "training?"
A perfect example of a gun which I would avoid decocking if at all possible is a revolver with a hammer shroud. OTOH, I feel 100% confident in my ability to decock the average modern handgun, safely, using the right procedure. In case you have doubts:
http://i688.photobucket.com/albums/vv241/gloob27x/DSCF4993.jpg
I absolutely don't trust myself to keep the hammer from slipping, and yet I decock this gun every time I load it and before each time I holster it while shooting.
BTW, I verified that the decocking lever only lowers the hammer to the half cock notch on this gun. If it lowered the hammer all the way down, I wouldn't have removed the lever. I feel 100% confident in manually decocking this gun to the half cock notch, but I would never attempt to lower it all the way (since it's DA/SA you'd have to keep the trigger pulled the whole way down).