Kettch said:
Jon himself thinks that it's breaking his vows
As I've said before and Maester Aemon said in (I think) the first book when he had "the talk" with Jon, a person might resist the temptation to desert for the first time, the second time, the third and even the fourth, but then maybe the fifth time will cause him to desert. He has resisted the temptation a lot, yes, but it's not that far-fetched to have him to do the decision he did after reading what he had read (Stannis dead, one person Jon put a lot of faith behind of, "Arya" on the run and possibly in danger, Night's Watch in danger if Jon just stays there). It essentially shows that Jon isn't the kind of "perfect" protagonist fantasy stories have and some people have been complaining him of being.
1) That's what anyone in the Watch would think after hearing him read that letter. Regardless, he basically tells them that he's breaking his vows and abandoning the Watch. "The Night's Watch takes no part in the wars of the Seven Kingdoms. It is not for us to oppose the Bastard of Bolton...I mean to make him answer for those words, but I will not ask my brothers to foreswear their vows."
Again, I think he knew very well what kind of hopeless mission it would be and thought that if or, rather, when he'd die during it, that would be his punishment for "deserting" the wall. A punishment he'd be glad to take if he managed to save Arya.
2) It doesn't matter if it's the best decision when he knows how prejudiced his brothers are. There was absolutely no way they were going to stand being commanded by a man who made a name for himself by killing their fellows.
Wasn't a lot of the force going to Hardhome going to be wildlings anyway? It was mostly going to be wildlings saving wildlings, but with some support from Night's Watch. It could've caused trouble if a few NW brothers tried to give some stupid orders in a harsh situation and with wildlings disobeying.
If he wants a suicide mission, there are better ones to go on. To Hardhome for instance, would be easy to find a way to get himself killed there and he would be dying for the Watch instead of as a traitor.
Hardhome wasn't as much of a suicide mission as going against Winterfell with a small band brothers from Night's Watch. Also, Jon had been obsessing about Arya throughout the book (especially after Melisandre gave that "false" prophecy). For all Jon knows, Arya is the only living Stark and maybe he thought it'd be more important for him to at least try save her than for him to stay as the Lord Commander of the Night's Watch (or alive).
Also, if Jon had gone beyond the Wall, that would still have maintained Ramsay as a thread to the Night's Watch. By going against Ramsay himself (and whoever might've joined him), that could've saved the Night's Watch.
, which is why I can't understand why this is apparently more important than his father being executed, than his brother being murdered, than his sisters being held captive, than staying true to the woman he loves, than being able to unite the North by taking Winterfell as Stannis offered or than his sister being wed to a lunatic.
Since becoming Lord Commander Jon has shown such remarkable sense and restraint when it comes to baiting, yet this one letter completely sets him off. I really don't get it.
Again, a man can resist temptation until there comes that final thing that pushes him over the edge. Yes, his dad died (what could he do so far from him?) and his brother went to war (he DID desert the Night's Watch then, if you don't remember, Mormont just decided not to punish him for it because his friends brought him back quickly enough). Yes he had a crush on Ygritte, but at that time he just simply got a reason to return to the Night's Watch after he saw the wildlings kill a person mercilessly. He didn't want that to happen to his brothers, no matter if he had had sex with one of the wildling womans. Had they not done that, maybe Jon would've been too far along to do anything about it and really become a real deserter (or done something too late, dying in the process). His sister was captive, but as far as he knew, she was in no immediate danger and was being treated decently. He probably didn't think, as a bastard, that Winterfell was for his to take. Also, he had just been voted as the Lord Commander. His friends (or mostly Sam) had gone through a huge trouble to make Jon the LC, at that point he probably thought he had the obligation to stay there instead of being all "lulz, thnx but no thnx, I'll go rule Winterfell instead" (besides, he knew Winterfell was in ruins). As to the last point, did he know how crazy Ramsay is? Maybe he just thought it'd at least be good if SOME Stark is in Winterfell, a marriage should keep Arya at least somewhat safe.