Everyone engaged in the public discussion of football is now vulnerable to the lunatic fringe.
The internet drives much of the madness, as an academic, William Hughes, observed in a recent review of a book about fandom.
'The internet isn't just a space where fans debate with one another,' he wrote in the London Review of Books. 'But also where tribes build up a distorted and hateful picture of our enemies.'
Which brings us to the top of the West Stand at the Emirates at around 6.30pm on Sunday and Roy Keane's encounter with an individual who, judging by the grainy footage, was not there to discuss the respective merits of Rasmus Hojlund and Eddie Nketiah.