Many believe it is imperialism, or nation building, when we jack around in the Middle East.
What the strategic value really is:
With most of the world's oil supply in the ME, then whoever controls the region, in essence, can control the world. It is easy to say that since we are now producing 100% of what we need to consume, and can for the next several decades, then it should not matter, but it does.
Why? Because, if Russia were to control the oil, then political leverage would be easy. Prices could be manipulated with ease....what would nations pay for oil? Any oil? Would they give trade concessions? Would they bow to political pressure and end NATO, or more, end diplomatic relations with the US? How about simple trade? Crash our economy. So the US could bridge the gap in oil, but for how long? Our own domestic security demand that we do not export oil as we did in the first half of the 20th Century.
If China were to gain total control of the oil, same consequences. Different partner, same objectives.
Remember, Russia already controls the natural gas supply for Europe, and they can shut the valve off any time they wish to create chaos in the populations.
Now, all that aside: Why is it important to retaliate?
One, it is absolutely necessary to instill fear of retaliation for any nation, or any group to use chemical weapons. Since ISIS and it's affiliates cannot manufacture the gasses, then they have to rely on a nation state to produce them, and if you make the nation state pay a cost for engaging in poison gas trading, then in theory, you make the cost to high.
Two: Reagan beat the Soviets in a phantom arms race to the top....if Russia presents a real threat, then the same objective is in play. Crash their economy.
Three, and maybe most importantly: It is the moral thing to do. It sends a strong message, and insures we remain feared. We are not the World's policeman.....and we certainly have no real friends, aside from Israel, but we cannot step back to the 1920s and Isolationism.....it led the way to WWII.