Twinklemegan's points about society/MN expressing horror, rather than grief; and about us all 'owning' this (and haviing to take responsibility for it) are v interesting, I think.
I do think it's horror, not grief - whether or not the individual grieving posters would agree.
The knowledge of terrible truths is a dreadful burden which we usually try and leaven by sharing, because it's almost impossible to contain and process horror individually.
Cultures have historically found ways to allow individuals to express their terror at the madness and randonmess and cruelty of life publicly. (You could argue that horror films, for example, exist to do this job for us - they translate the horror we know exists in the world into images and words, and in watching them we process and contain our horror at real life events.)
In some respects this stops us being angry enough to force change, but in others, it allows us to live in a world in which inexplicable acts of cruelty occur.