So you honestly believe they brought Jon back from the dead, made him a descendant of the two oldest most legendary families who also happen to be the only families tied to magic, and have made him the fiercest warrior in the show (all the other names mentioned built their reputation during Robert's Rebellion, in this story Jon is the most legendary warrior by far), just to kill him off for exactly the same reason he was killed for before, or to be ruled by someone else? That would be one of the worst character arcs in literary/television history. He's not the leader Westeros/the North deserves (they deserve a cold hearted scumbag), but he's the leader they NEED, in that he's willing to look like a fool and put himself in harm's way to do the right thing, and only a person like that can unite enough people to even have a chance against the White Walkers. Prior to the White Walkers those qualities would get a person killed, but now that they face a mutual threat of total destruction a person like that is necessary. He's not too stupid to see his mistakes, he knows full well what he's risking, he just knows that if he doesn't risk everything he'll end up dead/a wight anyway, along with the rest of the world.
Remember this is a fictional story, there's a reason a b*stard/underdog was put at the Wall. To the other characters he's a nonfactor, but to the reader/viewer we know he's been involved in the only battles that actually matter, and in the end he's most likely gona be a pretty typical hero in that he rose up from nothing against all odds, had fate (in this case magic) on his side, and helped the people overcome a seemingly invincible opponent. George RR Martin might mix it up by killing Jon off at the end, or killing everyone off, but the overall themes are still pretty stereotypical.
