[cookieperson]

That's part of it. There's also the risk of clandestine operators discovering easily made chemical weapons that do not require a professional lab to create them in bulk. A nation state, or well funded terrorist group could exploit such a thing without too much effort.

It's important to remember. Chemical warfare can be used for mass destruction, but this approach could be used for other nefarious things at smaller more discrete scales en masse. ie 1000 attacks with different agents in each one... Forensic nightmare.

I like your suggestion to counter these things, but, these are predictive tools. They can and often are or will be wrong. False positives would be a real problem. Again though the people interested in doing this won't be dialing up a chemical supplier to do it for them.

[Pet_Ant]

...also can't these be used as insecticides and other beneficial things?

[cookieperson]

Sure maybe some of them. That doesn't make a threat actors pursuit of weapons legitimate though.