Shooting with one hand is not really that difficult, though I will admit that very few of us will get as good with one hand as we are with two. However, this being said, most of us can get good enough to defend ourselves with some practice and proper technique.
The most common technique used for shooting with one hand is to cant the gun slightly and step into the gun, using the upper body to help control recoil. While this does help, I have found that there are a few potential drawbacks to using this technique exclusively when shooting one handed.
We need to think about what the circumstances will be in which one hand shooting will be used. Two situations come to the mind of most officers: when one hand is injured and when the engagement is quite close.
For close-quarter situations, does it make sense to step into the suspect and outstretch your arm? If the suspect is close, you run the risk of placing your gun within his or her grasp. If you try to pull the gun back to shoot in a close retention position, your forward step will place you too off balance to repel the attack since there will be nothing behind your upper body to help retain balance. Again, not good.
I teach a one-hand shooting stance that is a bit different than what is normal and I have had a great deal of success with it. In reality, it is not much different than the stance that many people use with two hands, which makes it quite easy for most people to pick up quickly.