We don't concede many goals (Brighton aside). Kilman can defend and isn't out of place in the PL he's just not a top half player which is where we want to be and he can't carry a defence he needs a stronger player next to him.
It's the mistakes for me, just yesterday. Fell over and gave Antony a clean run at goal which he should have scored, their first goal he was badly at fault for too. He's not a complete liability but he's good for 3/4 mistakes most games and you can't have that at this level.