I disagree! The people he killed were not innocent, they were part of a joint enterprise to murder Ellie. If Ellie wanted to be sacrificed then the Fireflies could have sought her consent, but they didn't, instead the deceived her. Perhaps they were overall justified in murdering her because the stakes were so high, but its a stretch to present them as innocent! Many people would chose to save a loved one in a situation like that, even if it would be hugely detrimental to humanity as a whole. Joel's deception of Ellie was more problematic in my opinion, but not monstrous.