I can understand the criticism of Warner's choice to stay in the game. Beign a mild concussion he may have thought it was not a serious injury and just had the attitude of playing through it till the half. Halftime being according to the news when he told the trainers about his problem and they cleared him to play (with a concussion???).
At that point the responsibility of the coaching staff and trainers to protect the player is where the blame rests. They should have known better than to continue playing someone in his condition. Let alone, continue to call passing plays when his head is already banged up. Especially with Marshall Faulk in the backfield. Especially with Marc Bulger on the sidelines. Warner should've been given immediate medical attention right during the 3rd quarter. I wouldn't fault him for playing with his injury when his coach and trainers cleared him. Players develope a trust with their coaches and trainers. They expect and trust that their trainers will not put them in unnecessarily dangerous situations. Similarly, players develope the attitude of listening to their coach, and trusting in their decision making. If they didn't you'd see Linebackers and QBs changing the called play at least once every drive of every football game.
That being said, faulting Warner for playing a terrible game is a bit harsh. The man played football (almost entirely a passing game on offense too) with a concussion for over half the game. It's remarkable that he managed to throw over 300 yards and average over 10 yards a completion when you consider the fragile state his mind was in. He had gone to the trainers, they cleared him, the coach cleared him. Any player who cared about his team would be telling himself its all in his mind or must've been something they ate at that point, because otherwise the trainers would've caught it.