President Obama is hardly alone in drawing a "red line" through the use of chemical weapons. The international community has long considered them to be beyond the pale of warfare. Here's why.

Just how bad are chemical weapons? Really, really bad.

President Obama has said that if chemical weapons are used in Syria's civil war, which has already claimed 70,000 lives, the United States may have to intervene militarily.Obama is hardly alone in drawing a "red line" through the use of these particularly gruesome weapons. The international community has long considered chemical weapons to be beyond the pale of warfare.British troops blinded by tear gas during the Battle of Estaires, 1918. (Wikimedia Commons)What makes them worse than other methods of killing?One ...