The main reason it should be banned is because many people die and the ones that survive have no-where to live and have no-one to look after them (families are turn apart). It costs alot of money to then replace the homes that are destroyed by the bombing.
The Charter makes clear that the U.N. Security Council can choose to authorize the use of force. This further weakens the understanding that war is illegal, by making some wars legal. Other wars are then, predictably, justified by claims of legality.