Fair enough - but the argument seems to be akin to continuing to hire a surgeon in the same role after he has lost his sight as the result of an acid attack.
I think most feel bad for Diaby and the aftermath he faced as a result of that POS all those years back. Had footballers not been so richly rewarded, I'd expect and attend a testimonial for him, but he is set for life. While that can't cushion the blow insofar as regret he'll always have for not fulfilling his potential, he is luckier than most and has been given every opportunity by the Club. It is not as if they left him lying on the pitch after that tackle - and neither did the fans. But surely now - it is clear, he can't fufill his role and everyone needs to move on.