I think people can accept one off mistakes or poor judgements - however, when the man makes the same stubborn obvious errors over and over again with little cause to hope he'll change, then people will come to the conclusion that he's been found out and is out of his depth.
It's such a massive shame as if he had man management skills and a bit of flexibility, he could be a top drawer manager. But the situation with Howard is just the latest in a long line of errors - having team favourites is always a bad thing, as you should be looking at form first and foremost. Combine this with his "philosophy" which has been utterly found out in the Premier League and having him in charge is a disaster.
The matchgoers turned on him en masse at Leicester and in my eyes he's a dead man walking. I think he'll survive until around November sadly, but I can't see any chance of things improving to the point where he should keep his job and, indeed, should have been dismissed in January after the WBA result.