I was looking at some flight paths, and I noticed that while some airspaces are ignored by planes for "obvious" reasons, like the Ukraine - Russian border airspace.
For example, this flight seems to purposely ignore the Ukraine airspace.
But on the other hand, I found some flight which are not ignoring airspaces which should probably be ignored. Like planes flying over Syrian airspace or over Yemen. These places too are war zones and might have militant groups capable of repeating something like MH-17.
This made me wonder as to who decides what airspaces to not fly over, and what are the criteria to do so?