Indeed, but players are also human beings, and mostly spoilt ones, they make mistakes. Sure if someone goes too far then there's no way back usually and as I said I don't care much here (though he could have dealt differently with it publicly).
But SAF didn't release Scholes when he refused to play. He also had a lot of patience at times when Rooney (when he was young and a great player) was off partying and / or off form and instead we heard by SAF how he had a virus or was injured. There are lots of other examples, too with players. It will be seen if LvG has done that with Valdes because he is not that important and will deal differently if a more important player behaves like that or does something stupid.
Obviously LvG has to deal with stuff like that, but do it internally and only in public if he wants to acchieve something specific by it. You just can't in every case call out for a player in public and leave yourself and the player no way back if a mistake by the player is made, that will be very costly for the club if a more important player is involved and let go as a result.