... because it has a kind of just irony to it that made it very enjoyable.
A musician, Cain, comes to Dodge City on the stage and goes to see Doc Adams. He is dying of heart disease and has only a short time to live. He's a rather small likeable fellow, rather cultured, not from the west at all, but headed for Arizona. As an aside, perhaps Doc Adams is the reason that HIPPA privacy regulations came into being, because the reason the audience knows all of this about Cain is that Doc is talking to Matt and Kitty about the details of the case. If there had been X-Rays at the time I wouldn't be surprised if Doc and some stray cowboys would have been discussing Cain's internal organs over a beer. But I digress.
But suddenly Cain changes his plans, decides to stay on in Dodge AND he buys a gun and gets Chester to show him how to use it. Matt is perplexed and goes and asks the guy why he bought a gun. Cain is not forthcoming at first, but then he finally tells Matt that he plans to kill a gunslinger and gambler around Dodge named Adams. Cain says he realizes Adams (no relation to Doc Adams) might kill him in a gunfight, but he might also kill Adams if he sneaks up on him and shoots him in the back. Matt mentions he will hang for that. Cain says that he will die in two months time anyway so what does he care. Cain says he has his reasons for hating Adams enough to kill him but will not state what those reasons are.
Matt does warn Adams about this, not because he likes him, but because it is his duty. It does make Adams nervous that somebody might come up behind him plus he has no idea who Cain is. Let's just say psychologically Cain plays Adams like a violin. You just don't see this kind of rather complex irony on Gunsmoke that often.