The Red Wedding eliminated the entirety of the Northern Army. With it, the Starks, the only "good" house, who weren't even fighting to conquer the Kingdom, where all but eliminated. One was already being corrupted, and the others taken out of the country. So yeah, it kind of killed all the good guys.
1. There are no hard and fast rules of storytelling when it comes to the plot and characters, that's up to the writer. Rules exist only for clarity of presenting the information. (Like including foreshadowing, or varying the pace to keep the audience's interest, or the guideline of try to tell things in sequential order, for instance)
2. In SoF&I, the AUDIENCE knew full well pretty much the entire family was alive. And that it plays to the STORY for the characters to think the entire family was dead and react accordingly
! Rob is the only "main" character that died during the Red Wedding, and he NEVER had a POV chapter. So, he wasn't even a main character, he just had some plot importance! He was second fiddle to Cat's story! His army? Plot, but not important to the overall story which is much bigger than a single person or army, much like an actual history.
! Aside from that, Daeynarys, Tyrion, Jon, Bran, Sansa, Arya, Theon, Davos, Jaimie, Samwell, and Brienne were all alive and kicking, and they were definately all main characters, and aside from Jaimie, they'd all be considered Good. Plus about a dozen minor POV characters. on the side. Red wedding despite its shock value, didn't kill anyone important, (which is obvious in hindsight, again, Rob never had a POV chapter) it just set other story points in motion.
! Martin is telling the history of Westeros, not the Tale of The Noble Starks. You want squeeky clean heroes that always win and never die in a "go fight the cosmic evil" typical fantasy, you go to Wheel of Time. Completely different story goals there.
(Also, judging by your reaction to the Wire… It seems you feel like a character dying suddenly makes for bad storytelling, regardless of what actions might have led to it, or what the follow up reprecussions might be?)
And I never said you can't question it. I've said time and time again that you can! All I'm saying is that just because you don't agree with it can you accuse Oda of having made a mistake with the story. If he is telling the story he wants to tell the way he wants to tell it, then it's all correct. That doesn't make it perfect, that doesn't make him perfect. I feel like I've said this blatantly a million times by now, but you keep not getting it.
Oda makes mistakes all the time. Thats why he has corrections in the tanks.
Also, the sheer nature of an ongoing serial (in any medium) that puts out chapters before the entire story is done denies you the ability to properly edit, so you''re stuck with whatever you put out, regardless of if it is what you really want by the time you're done, or what you know would be better for the overall story with hindsight. (Added scenes, deleted scenes, more setup for a thing, less setup for a thing, more time for a certain character that ended up being important, less time on a throwaway, etc.)
I'm sure Oda has chapters that are his favorites. I'm sure there's also chapters he hates that just didn't come out like expected, or didn't pay off how he wanted.