People need to calm down. This is more like criminal negligence than an act of war, and the response needs to be on that level.
Like most disasters, this is most likely the result of an accumulation of unrelated but serious mistakes by multiple parties. The obvious culprits are the Kremlin, for not understanding the risks of having sophisticated weaponry like this in the hands of irregulars, and the ICAO, for allowing civil aviation anywhere near that area.