If you are referring to the use of Agent Orange, it would not be considered chemical weapons attacks because the intended targets were not people, but trees. At the time Agent Orange was touted as safe for people. Soldiers frequently went through areas hit by the defoliant chemical. As a chemical weapon Agent Orange would be classified as ineffective against people since the harmful effects do not show up until years after the exposure.
Your argument is akin to claiming construction workers and ship builders until the early 70's were being deliberately attacked because they were constantly being exposed to asbestos.