As my humble counterpoint
Whilst I don't particularly like Facebook - but I don't think they're to blame for this pool of excrement murdering a lot of innocent people.
Maybe more pertinently (or naively) I can't believe that anybody who saw this video would be swayed to join his cause - In much the same way I doubt watching an ISIS beheading would inspire us all to all go off and fight for the caliphate.
"Think of the Children!" is a worn out trope, and can't just be appropriated from ridicule when handy to your current thinking.
A lot of current news-stories seem to be covering "ironic-racism" as a 'cover', a 'gateway', a 'tactic' to win people over - and my own view is that hiding/censoring/whatever information plays into this strategy. Just show the scum. Show everything. Make people watch and pick a side (we all know once sides are picked, we become inoculated to argument).
When I become benevolent dictator of the planet, the day after a similar act, your facebook landing page will run this footage in the centre of your screen. Maybe on one side it'll show the 'lolz and memes' of the shooter, and the other, on every f'in shot it will pause and play back one of those saccharine auto-montages of the life that was just taken.
Facetious, yes, and I wish I had a cleverer way of presenting my point - but telling the world "49 people are dead" misses the point.
Something Facebook might actually be good at doing - show that these weren't "49 deaths". Show these were 49 individuals, with even more than a name, a religion and a stock-photo. People posting pictures of their cats, planning a cinema trip, trying to get more than 4 people to turn at at a place at a time and all the rest of the banality that is actually relatable to.
I loved that when you wrote this story you deliberately didn't mention the fuckers name. Next step on this path is to mention every name of all those he killed - and give them the voice that he took (even if it is a picture of their cat pulling a silly face).