100% spot on.
I suspect what is happening here is Stux is actually a good person. Like any good person you hear about the death penalty and you are appalled. He has an emotional reaction (a very justified one). Then in that state he hears about gassing, and rightfully associates it with Nazis. He should be associating the murder with nazi's but the gas part is what stands out for some reason. So now he is offfended at the gas choice, in reality I think he is just offended by the murdering and the association with nazis is just too easy to make the association even though its not the part that matters.
Stux has the tendency to get a little emotional when literal nazi shit is going down, and well, can we even blame him?