That's not at all why it's banned in war. It's banned because the opposing side might mistake it for something like nerve gas, and then respond with something like nerve gas. Important to note that the chemical weapons treaty does NOT ban chemical weapons in war, it bans "first use."

(source, I took a class on Bioterrorism at RPI, which is still being taught apparently: http://catalog.rpi.edu/preview_course_nopop.php?catoid=8&coi... )