There's no "thinking" about it. The facts are the facts. What he did was against the law, pure and simple. An honor code is just that, a code, a highly subjective set of rules of conduct that different cultures define differently. An honor code is not the same thing as the rule of law as codified in instruments like the Geneva Conventions. For instance, a Marine wouldn't be tried in court for leaving behind a squad member, even though doing so would break a deeply held honor code among Marines (and other service branches, obviously).

While the law is subjective -- otherwise, why would we need lawyers (some would argue, rightly in a lot of cases, that lawyers do more to obfuscate and frustrate the law than they do interpreting it, the DOJ under Bush being a great example, e.g, Gitmo) -- the fact is all soldiers and contractors operating in a combat zone have to operate under the law, regardless of what the enemy does.

Does it hurt our COIN efforts? I would say yes. This specific incident? I don't know. This incident paired with other incidents like it (PMCs firing on civilians in Iraq, the Gitmo disaster) have a incredibly deleterious effect on COIN efforts and America's standing in the world.