I have to put out a short rant here. Modern handguns often include a decocking lever of some sort to allow you to safely decock the pistol without requiring the user to pull the trigger. This has a few benefits, including the dropping of the hammer in such a way that none of the usual trigger safeties disengage when the hammer drops.
Unfortunately, there seems to be another trend that I've noticed. Perhaps it stems from my limited experience and perhaps because of my slightly different training that I received when I was first learning guns. However, when I was learning how to shoot guns, the decocking lever was not nearly so common. So naturally, part of my education was the proper decocking of a handgun.
I'm sure there are many schools of thought on this, but today I see all over the Internet people talking about how much they like their decocking levers because of the danger of decocking without them. At this point my warning bells and alarms go haywire. If your manual decocking method is that dangerous, you're doing it wrong.
Simply put, when you deal with a gun without a decocker, you should be able to decock that weapon with as much safety as if you did have a decocker. One of the issues with striker fired handguns is that you cannot decock such handguns with nearly the level of safety that you can a hammer fired gun. I define safety here in terms of the number of barriers between the user of the gun and a negligent discharge. That is, just how many things does the user have to mess up in order to accidently discharge the weapon while decocking. On a striker fired handgun without a decocker, there's simply one barrier: making sure the gun is unloaded.
Putting striker fired handguns aside for the moment and considering the hammer fired versions, which would include many/most revolvers, and a significant number of semi-automatics, the method I see almost universally online is for the user to place the thumb of their weapon hand on the hammer, and then to pull the trigger, slowly allowing the hammer to come down from that position. If we examine this, however, it becomes obvious why people who decock their guns in this way often feel that a decocking lever is safer. If their thumb were to slip, which is a very very real possibility, then there is nothing in the way of that gun firing as normal.
How people manage to think that this is a good idea astounds me. If this is how people decock handguns, no wonder they want decocking levers. It is an accident waiting to happen. The solution is simple. When decocking a handgun, take your support hand and wrap it around the gun, providing further support, and finally, interposing your support hand thumb between the hammer and the firing pin area. That thumb should cover the point where the hammer will fall. You then proceed as usual and slowly release the hammer down with your weapon side thumb in a controlled manner. If your weapon side thumb should slip, the hammer will strike harmlessly on your support hand thumb, and nothing will happen. The gun will then be in a half cock or near half cock position. You can then regrip the hammer with the weapon hand thumb and continue your action. If your thumb does not slip, you can remove your them slowly from that location and let the hammer slowly come down while still retaining firm control with the weapon hand thumb.
Since the support hand thumb is much less likely to accidently slip, and it's not likely at all that both hands will sip at the same time in a catastrophic manner, this is significantly safer than the alternative methods, and greatly reduces the perceived need for a decocking lever. Don't get me wrong, I like a decocking lever a lot, as it's a very nice convenience, but it is not a substitute for knowing how to properly decock a gun in the safest manner possible.