To me the worrying part of this is that at this point in time it seems that the flight was brought down by rebels. All instances of civilian planes being taken down in the past were military acts by national forces. That rebels somehow obtained the means to bring down a plane at cruising altitude is disturbing because this would mean that guarding the airspace directly around an airport is no longer enough to guarantee safe flight corridors.
It's also interesting to point out that when civilian jets have been brought down in the past, it was almost always(or even just always) a mistake as well; two examples:
- An American cruiser took down an Iranian jet in the past because they thought it was a missile coming at them due to its flight pattern on their target radar.
- A Russian fighter jet was looking for an American radar plane during the Cold War, but he mistakenly took down a Korean civilian jet(this was at night) which happened to be where they were expecting the scout plane to be. The flight had veered off course due to failing to set the correct heading mode on the auto-pilot.
So as you can see, while it is worrying that rebels have such weapons, military forces are known to make these mistakes as well(especially at times of war).