I remember following the Mairia Cahill case years ago. It wasn't written about much in the main stream news. There was a documentary about it, which came down very much in Cahill's favour. Greenslade was the media critic for the Guardian and claimed it wasn't good journalism, because it was biased. Cahill (and others) took that to mean that Greenslade sided with the IRA. The Spectator published an article about it a few days ago. I can't quote the whole article because the Spectator is behind a paywall, but I've read the gist.
An attempt is being made to smear Greenslade (don't know why) and the easiest way to do that is to accuse him of one of the things most of the public find abhorrent, which is to accuse him of siding with the IRA - and, yes, it's strange that loyalist atrocities are hardly ever mentioned.
It's the way the media works - not just with Corbyn or Meghan Markle. They find an Achilles heel and publicise it, so that the person becomes one-dimensional. Short slots on GMB don't have time to examine issues in detail and the majority of the public seem happy to accept their news in short sound bites. It's well-known that many people never read beyond the headline and subheading of a newspaper article.