In recent times, ISIS has vowed to kill anyone who does not conform to their ideals. These tactics have included torture and execution by beheading. In particular, Christians are being persecuted for their Christian beliefs, which goes against the beliefs of ISIS.
Additionally, ISIS has begun the process of using technology (such as the Internet) to recruit Americans to travel abroad, train in their camps and facilities, and use that training to inflict terror all over the world.
Based on the extreme ideology of these people, diplomatic negotiations are not an option and the President is strongly urged to kill and destroy these people by any means necessary. Air strikes, boots on the ground, etc.