You are all as bad as each other, both sides
The American military is merely a tool that is used by Washington to further its foreign policy and political aims, you can't level the generalisations on here without looking at the bigger geo-political picture.
That being said, clearly an innocent person died at the hands of an American serviceman/contractor due to a combination of negligence, arrogance or pure chance, in any sense answers will be sought.
The American military in recent history (the last 30-40 years) has undergone a transformation in the sense that the difference in the quality of the best and worst has increased.
Many of the enlisted recruits that end up in basic infantry combat units come from poor backgrounds with a relatively low standard of education. Conversely some of the finest combat units in the world today exist in the US military.
The upshot of all this is that for better or worse, the US military is judged by its worst, rather than its best.
In the instance of what happened, I have a sneaking suspicion that it will come pass that whilst the rules of engagement were followed there may be repercussions in terms of procedures and the application of the ROE.
Was it murder? no, was it manslaughter? probably.
America's biggest problem, when viewed from the context of being outside of the inward looking 50 states is that whilst it preaches Justice and fairness, it's actions say otherwise.
I have been fortunate to have lived in the USA, I have served alongside the US military, you will not find a more generous, noble and honourable group of people, unfortunately they are continually let down by poor leadership, entrenched views and a collective unwillingness to accept that not everyone views the world in the way that they do.