One thing you have to remember about the word "murderer" - it's a word with both moral and legal implications, and shouldn't be thrown around as lightly as it tends to be (at least online). It's not a word that you use for anyone who has ever killed a person before. You don't call someone who fought in a war a murderer (at least I hope you wouldn't), because calling someone a murderer is saying that what they did was morally wrong and that
they deserve to be punished for it.
So, the question shouldn't be "is Sora a murderer?" It should be "is Sora a killer?" (Which, usually, does not have the same connotations - someone can be a killer without being a bad person - see the soldier example again)
It's more interesting to think about it group by group, though, considering the relevance of destroying Heartless, Nobodies, "unlocked" people like Maleficent in the first game, etc.
Heartless, I think, probably don't have much moral weight at all. While they might have been a part of someone that was transformed, they really aren't anything like a person. They're basically a big ball of heart-seeking instinct and reflexes, and thus, probably not sentient. Also, destroying Heartless actually makes it possible for the original person to come back, which is a good thing. Sora's probably as much a killer for destroying Heartless as you would be for taking an antibiotic, really.
Nobodies are more tricky. The game doesn't help this by having the character who says the most about what Nobodies are be someone who'd have reason to fudge the facts to suit his own ends - I don't think we can take proclamations like "Nobodies do not deserve to exist" as fact in the KH world. Yen Sid is a more trustworthy source, but even he's brought into question by having his explanation placed right after we've been with Roxas for two hours in which this explanation was challenged.
Ignoring the game's conflicting hints, we still can pick some things up about the Nobodies that could help here, though. They can think and plan, they're self-aware, and, unlike Heartless, they're sentient. They might not be people, but it'd be far easier to argue that there's something there that could be killed.
Of course, this is complicated by the fact that the destruction of a Nobody is necessary for the Nobody's Other to be able to return. I don't think this would really affect whether killing a Nobody would make you a killer (though it might affect whether killing a Nobody would make you a murderer), though.
The "darkness unlocked" people are a pretty interesting case, too. The best example is Maleficent, considering that her darkness was literally unlocked by Ansem-Riku's fake Keyblade. Dragon Maleficent seemed to act like a Heartless. Unlike a Heartless, however, she wasn't just part of a person - she was still all herself, just taken over by darkness. If she wasn't somehow resurrected, she'd probably still be dead, unlike the Heartless, whose destruction enables the person to come back to life.
Actually, this kind of fate probably makes more sense for Clayton and Scar than actually becoming Heartless - after all, Xehanort was supposed to be the only one who retained human form as a Heartless, and Scar ended up as a ghost (which shouldn't have happened had he actually been defeated as a Heartless). Perhaps this is what happens to those whose hearts are eaten away by the darkness rather than simply being stolen?
The problem here is, while the thing that Sora killed probably wouldn't have much weight on its own, it necessitates the death of the person who was turned into that, which could be reason enough to call him a killer for it.
Then, there's the final example, which is someone who was actually a person that was killed by Sora's group - Shan-Yu. Well, it is possible that he was in the "darkness unlocked" group, but it's never stated out loud, so, I'll ignore that possibility.
So, basically, you probably could call Sora a killer. I don't think he ever really did anything wrong, though, considering that everything that he killed was trying to kill him first.
...well, apart from Demyx, but even that was in the heat of battle.
And, some responses to things in this thread I wanted to respond to:
Meh. I wouldn't consider it murder. When I think of murder or killing, I tend to imagine a bit more gore and such. All the heartless do is just puff into black smoke and release munny and HP/MP orbs.
...that's certainly an interesting definition. xD I don't really know if it works, though; Final Fantasy X monsters disappeared into pyreflies which basically showed that they were killed and sent off to the Farplane, for instance, which is kind of a reversal of that.
ohh i see what you mean now about the DN thing. Yeh, I suppose the moral is similar and whatnot, like is it right to kill someone whose done wrong.
...actually, I'm pretty sure the moral question at the heart of Death Note isn't really whether it's right or wrong to kill someone who's done something wrong - it's about who has the right to enforce that, or at least, that's what it becomes. There's really nothing in Death Note that suggests that the death penalty is wrong, just that taking justice into your own hands is.
And that's not really related to Sora's case, because he's not out looking for bad guys to kill; he's trying to protect his friends and fighting for his life.
Disney would lose their franchise and popularity if they made a children's video game with a goddamn murderer as the main character.
So no.
This little cartoon character doesn't actually kill people.
Game wouldn't be rated E or E10+ if he did.
=/
And if he did, Disney would lose a helluva lotta cash.
E/E-10 ratings are based on a lack of anything graphic, not necessarily a lack of killing. I'm sure there's lots of strategy RPGs out there where your little people kill lots of other little people that are rated E because nothing bad is actually shown.
And if you think killing = murder, than Disney's already got away with that lots of times in their G-rated movies. Mulan's the best example (think how many Huns were killed in that avalanche).
As for Sora being a murderer by 'killing' members of the org.13, if you remeber that in final mix, namine tells sora that axel has not 'died' but has returned to become the person he once was, a human. So Sora is kinda doing the org. a favor don't you think?
That's not from Final Mix, that's from the KHII novels.

Still can probably be used.
Not really sure if Sora was doing the Organization a favor, though. They do have personalities separate from their Others which would get forced under - they wouldn't really be the same people. Though, Roxas and Namine did seem happy enough about it.
i would say...he is a murderer........but not the bad type...........
the one that Saving the World kind of Murderer.......:bored:.......but the true answer.....
yes.
enough said.
There is no "saving the world kind of murderer" or "not the bad type [of murderer]." The very meaning of the word murderer rules these things out.
Sora just kills everything without feeling anything >_>
Re-watch Sora's reaction after Xigbar, Luxord, Saix, and Xemnas' first two deaths, and tell me if you still think that.
If you good defeats evil that is not murder. (keep in maind I am talking about videogames here) .
Why limit it to video games? It's the case in real life, too. If you shoot someone who's threatening to kill you and your family, you wouldn't be convicted of murder.
Just to point this out to people who may not have noticed this yet. What the hell is the point of this topic? I mean it's like disscussing what happens when you fall into a black hole. nobody really knows for sure wether Sora was "Purifying" the worlds or what not I quite frankly i don't think anyone really cares.
This does though bring up a familar topic that I read once. "Sephiroth is made of three moogles standing on each others shoulders. Discuss..."
I mean this discussion is really pointless. It's amazing anyone actually replied to it.
Pointless or not, it's fun to speculate. ^^
And I bet someone could give you some fairly good evidence for Sephiroth being made of three moogles standing on each others' shoulders. XD
If you mean people as in just a body and soul, then yes. Sora's a murderer, and deserves to go to hell.
...woah, that's a bit much. o_o; Do you think every person who's killed in self-defense deserves that?