As often as he is now? Palace, Watford and Newcastle have had 6 shots on target combined, we conceded 5 goals. I think if anything, the defence looks worse because of him.
I also wonder about their confidence in him. His erratic nature means they never know if he's gonna come hurtling out, stay rooted to his line, jump around like a mad man, roll it out to them or smash it long and out for a throw in under no pressure. Say what you want about Howard or Joel, but their communication with the defenders and for the most part, their consistent behaviour, at least let them roughly know what to expect.
Ive lost count of the games that we have dropped points in where the opposition has scored with all or practically all of their shots on target and or he has been responsible for the goals conceded. It's not a witch hunt, it's just blatantly obvious what the problem is.