Improvised protective gear might well get you through a VX attack unharmed, Sean Connery and Nicolas Cage antics in The Rock notwithstanding. Staying indoors would work even better. Once the attack was over, in many cases you’d be able to escape the area with no more than a pair of wellingtons. I’m not saying that a chemical attack would be a completely trivial matter, but it would almost always be preferable to being hit by the same weight of high explosives.
So, if your aim is to kill and injure as many people as possible, you’d be a fool to use chemicals. And yet chemicals are rated as WMDs, while ordinary explosives aren’t. So too are biologicals, even more amazingly. Biological “weapons”, in the modern sense, have yet to be even demonstrated.
I’ve long been of the view that chemical agents are more weapons of mass propaganda than real threat. The Tokyo Subway Attack, for example, involved five separate releases of gas, under ideal conditions for a gas attack, and killed just twelve people. Tragic for those affected, but far less deadly than a bomb or even an accidental fire.