NonCredibleDefense

Far from useless against unprotected troops - especially in area denial and degrading enemy combat effectiveness. The real issue of practicality is that they're a matter of mutual deterrent - if Side A starts using chemical weapons, Side B may decide to start as well. But as you mentioned, we've solved the issue of protective equipment pretty thoroughly, so in all but the most lopsided of conflicts (Iran-Iraq War, Syrian Civil War, police against protesters), escalation does not actually give either side an advantage beyond the initial shock, and introduces a lot of unnecessary defensive and offensive logistics, the total effect of which is likely difficult to determine. How many millions of dollars of chemical shells are worth keeping a platoon of soldiers in gas masks for a few hours longer? How many millions of dollars of chemical shells are worth the enemy shelling you in turn and forcing you to spend valuable resources and logistics lines on NBC gear? Who comes out with the advantage in this asymmetric exchange - the one with more resources, or the one with fewer? Nightmare to tell.

Russia currently is using chemical weapons effectively in Ukraine - namely, tear gas. Great for disabling dug-in enemies so ~~mobik meat cube ingredients~~ mass infantry assaults can advance. We (the West) also use chemical weapons effectively - we claim WP as a smokescreen, but its application tends to be very, uh, 'dual-use' in smoking troops out of entrenched positions. In both cases, the effectiveness relies on deniability and prevention of escalation.

Disagree. Gas is perfect for underground bunkers. Being heavier than air it will sink down into the bunker and displace oxygen. Sure you can wear a suit, but for how long? And do you have enough suits for everyone?

On the bright side, think of how clean all our pools are going to be with all this chlorine everywhere.

Well, if there's an element of surprise you can do some serious damage. This is also why nobody uses bright green, smelly chlorine anymore. PugJesus covered the real logic.

You were close to right, though. Upvote just to offset all the downvotes.

Clearly you've never been in the military. Let's say the enemy one day drops leaflets saying they will gas your position every 12 hours at 8 AM and 8 PM every day. You're prepared with your gas mask and full NBC gear every 12 hrs. No danger at all right? Wrong. Even if nobody dies at all from the gas, the act of putting that stuff on twice a day will quickly give someone PTSD.

What if I forget or lose my suit?!? What if I oversleep my alarm?!? Are those army dudes at the treeline? I can't see out of this thing! I can't breathe! Fuuuuuck!!!!! The psychological effect is arguably worse than the weapons themselves seeing as the psych patients don't even have to be hit by it to feel lifelong damaging effects.