Perhaps, but I do wonder if it actually mattered all that much whether 8chan encouraged this. There's evidence of contagion in mass shootings, that shooters seem to see the headlines about a shooting and become inspired to imitate it. Maybe there'd always be mass shootings tied to 8chan so long as there were news headlines tying the previous mass shootings to the site and leading future shooters towards it. Those certainly have a much broader reach than anything on the site itself.