I've defended Pietersen before, but lets be honest he's an extremely difficult person to manage - highly temperamental, huge ego yet also a pretty fragile character. Also is very blunt and has no filter. It's inevitable at some point he will cause issues.
Looking back in hindsight I also don't think his heart was in it anymore, which is what started a lot of the problems with the management, and if that's the case probably best to remove him from the team.
For a rough timeline and what happened and who was to blame - I think in the lead up to 2012 when it all blew up it's clear he didn't like Flower and his regime and his eye started wandering towards the T20 leagues and to pick and choose his England commitments. This puts him at odds with the management and Strauss who backs them, plus sets him apart from others in the dressing room.
There is then the big blow up over his texts to SA players. Idiotic and self-inflicted and whatever his issues with team mates probably right to be punished, but I do think he had a point about the Twitter account and others like Broad were quite obviously guilty of also betraying trust in the dressing room and going against their team mates and should have had a similar punishment but it got overlooked.
The problems after that were because none of the previous got resolved. Cook just got him back in the team, only to sit back and let things unfold. KP comes back still not liking Flower's coaching regime, pissed off at management, and gunning for certain individuals. The "bowlers clique" (and Prior) obviously don't like him and are out of control with some of their behaviour. It didn't take long for it to go wrong again......
They had to try and get past it. New coach, new captain, KP out, Prior and Swann retired from that grouping. It was needed.
There was some pretty petty behaviour towards him though which you wouldn't expect from professionals in charge. When he got that huge triple century for instance and they rushed out a response of basically "great knock KP, by the way you're definitely never going to play for England again" seemed a bit of a cheap shot to me and not the way an organisation should behave.
No doubt he was a difficult character to handle and some of his comments to teammates were bang out of order but the management team should have sorted it out imo.
They could have gave him an choice, step out of line again and your out but they gave him false hope by saying “play CC again and if you score runs you will be considered” he did and then he was still not picked and IIRC he cancelled an 20/20 contract to play CC
No doubt he was a difficult character to handle and some of his comments to teammates were bang out of order but the management team should have sorted it out imo.
They could have gave him an choice, step out of line again and your out but they gave him false hope by saying “play CC again and if you score runs you will be considered” he did and then he was still not picked and IIRC he cancelled an 20/20 contract to play CC