You can't use a citizen's arrest where the crime is a property crime to justify using deadly force. The doctrine is pretty similar nationwide with Louisiana being a notable exception...generally speaking...you cannont KILL for property. That being the case, and stipulating that even displaying a gun is using deadly force, it is unreasonable to expect a private citizen to interfere in a property crime. The difference would come, if the citizen stumbled across a rape in progress or witnessed an act of first degree murder. THEN, I think, a valid argument can be made for intervening with a firearm.
"Common Sense?" Also known as "Horse Sense" is what keeps horses from betting on people! Sorry, but one man's "common sense" is another man's LUNACY. The law has to be the trump card. Now, I admit...in some cases, the law is bad. Bad law can be modified. STUPID people are forever.