Question, though: in all cases, the calculus of justifiable deadly force revolves around a threat to life or limb, yes? E.g., if the use of deadly force against arsonists is justified, that's only because of the threat to life or limb, not because of the threat of property damage? It's my understanding that questions of property damage or theft don't figure into whether it's legally justifiable to use deadly force.
As for whether it's morally justifiable, my take is simple: if I'm not physically present to protect the property, I lose the moral ground to defend it by any means other than the justice system. And if I am physically present, I'll use non-deadly means to protect the property, and resort to deadly force only if I can articulate a threat to life or limb. This position is very simple, but it satisfies my moral sense and my legal obligations, in the vast majority of situations I can think of. Am I being naïve about this?
A situation like Ferguson raises hackles on all sides. The only defensible reaction to all that emotion is to look carefully at the legal and moral requirements and satisfy them both. Emotions - even righteous emotions - are for feeling, not for reasoning or justifying.