The difference is that the New York scene produced Warhol and 4/8chan produced mass murderers. The intent and result matters.
But the chans are unique in that their culture (ironically or not) actively encourages and demonstrates the beliefs that lead to such violence. The shooter in this case mentioned having been inspired by /pol/ and mentioned the New Zealand shooter, who is being treated as a hero and a martyr by /pol/.
Facebook and other social media get blamed for passively encouraging violence and hate, while the chans get blamed for actively encouraging it as a cynical and ironic piss-take on society.