So the point had nothing to do with the children that were gassed (as Trump apparently lied about), it was about punishing the perpetrator? And we did that by not hitting the gas or preventing any more air-raids?
The point is when someone violates those agreements, you let them know you won't stand for it. Would you rather they keep using chemical weapons, and normalize the use of them by doing so?
Perhaps you don't know history very well. The Germans invented chemical warfare. Their reasoning for using it in World War I was that it would end the war quickly because it was so horrible. Instead, it caused an arms race as the allies quickly had to make their own chemical warfare program to counter the Germans. As the allies came up with defenses for their chemicals, the Germans would come up with a new horrible way of killing people. Got a gas mask that protects from one type of chemical? Then add in a non-lethal gas that penatrates the mask but makes the person vomit, forcing him to take off his mask and thus inhaling the lethal gas. This is the kind of shit the Germans came up with. Make no mistake, chemical weapons do not just instantly kill people like they show in movies. The victims are rendered defenseless and sick and in complete agony for weeks or even months before death. Imagine an intense burning sensation in your lungs and on your skin, and nothing can be done about it.
This is why the entire civilized world agreed to ban these weapons. You say torture is wrong to use on terrorists? Yet chemical weapons on civilians is just fine.
If we let these barbarians get comfortable using chemical weapons, they will all start using them. You think random AK-47 and truck attacks are horrible, wait until the Muzzies start gassing schools. Trump is putting these barbarians on notice, he won't tolerate that shit, even if you would.