Hat tip to "Dayuhan", ripped from a forum:
CW haven't deterred the Israelis from attacking Syria whenever they like, and they won't deter an American attack. They didn't deter the Syrians from rebelling. On the evidence of Syria, the track record of CW as a deterrent is pretty poor.
Indeed. Chemical warfare Armageddon scenarios didn't deter the Second World War either. The People's Republic of China even dared to intervene in the Korean War, opposing multiple nuclear powers in the process.
Maybe it is exactly the tabooing of chemical weapons which made them an ineffective deterrent (albeit CW usage was expected for WW2 in the 30's and WW2 still happened)?
Maybe nuclear weapons will sooner or later fail to deter war and nuclear powers will sooner or later fight each other on proxy terrain or on oceans because they won't think nukes would be used in such conflicts?
I hope to never learn the answer (and still hope for a long life, of course). Potential proxy conflicts should be taken seriously, as conflicts in need of defusing before the s**t hits the fan.