Once an army crosses the line, it ceases being a professional, disciplined force, and begins to resemble a rag-tag militant outfit
Counter-insurgency operations falter and become even less popular when the civilians that the army is meant to protect no longer trust that army. That is the practical reason why responsible armies around the world have strict rules of engagement, which prohibit the soldiers, regardless of provocation, from humiliating civilians, or using them as human shields. There is then the legal reason—using human shields contravenes the letter and spirit of the Geneva Conventions, which apply to all parties in conflict. There is also the moral reason—a national army is expected to uphold the highest standards and it cannot imitate the tactics or practices of militia, guerrillas, or insurgents. Once that moral standing is lost, once the legal restriction is ignored, then the objective, of winning the hearts and minds of the people, evaporates.