Professor X favours peace, but sometimes force is needed in order to ensure that peace is possible. Magneto favours force, but too much force can make things even worse. It's all about balance, not ultimatums. Force may sometimes be crucial in preventing further deaths and suffering, because every team needs both an offense and a defense.
Force is sometimes required to make peace. If force was never used to create peace, then the corrupt would always use force until they had full control. As long as corrupt people are in power peace cannot be achieved. Therefore a just society may sometimes need to use force in order to keep the peace.
In my opinion we should never use force to make peace. The reason is that it causes more bloodshed and suffering than if people unite and stand up against warmongers and tyrants. Sanctions and deterrents are far more effective and less costly than taking war to another shore. The key here is unity of spirit and determination for a cause.