We should use chemical weapons because it could save a lot more men then going into Syria. Chemical weapons are much stronger so it will do more damage and swipe ISIS out more. In two days, Jordan is sending 56 bombs to ISIS to try to lower the ISIS population. If we go in without chemical weapons then we would have to go in and lose a lot of man. Maybe going in without chemical weapons may save more Syrian lives but it won't take out as much of ISIS.
The simple fact that an agreement was set forward to turn over control of chemical weapons by Syria dictates the United States response. By that I mean, if they choose to disobey this agreement what other option does the United States have other than a retaliation? The United States cannot afford to look weak in the eyes of the world by allowing a much less powerful nation to dictate to the Unitied States.
The agreement to dismantle Syria's stockpile of chemical weapons is between Syria and the United Nations. If Syria refuses to comply with the terms of the agreement, it is not the United States decision on what the repercussions would be. The United Nations would need to decide on the next steps.