I think people who want him to stay are stuck in the past or are afraid to change, they just don't accept he's just not as good as they think he is. There's plenty of other options out there that could do equally as well or better, Henderson had a brief spell and already proved this to be the case.
Good shot stopper or not, his limitations have been brutally exposed in many matches this season, he looked comfortable against Forrest because they didn't press him, a week before Newcastle pressed and it worked for them. Even the Liverpool game, just look at the setups from the early goal kicks, it was clear ETH knew that DDG wasn't able to play through the press he basically had Martinez holding his hand. But even that didn't work. Sevilla did it too and he shits himself every time this happens.
Now that doesn't include his total lack of presence around the box, his weak aerial abiltiy, he's also not a vocal player which severley impacts his abiltiy to organise and control his defence.
I just can't see any positives to his game or any positives to keeping him, part of being a successful manager is knowing when a players time is up and they need to be moved on. Bigger and better players than him have been moved on unceremoniously, there's just no room for sentimentality at the top of the game.