Also, I presume you mean frozen CO2 going from solid to gas, and not liquid?
Carbon dioxide, despite being a fairly common gas, has at least one incredibly strange property, it melts at -56.6°C but it boils at only -78.5 °C (yes, I checked the temps). So before it melts it boils off. It cannot, under normal circumstances, be a liquid. going the other way it goes through deposition, again no liquid state. When he says sublimation its turning from solid directly to gas, for oxygen that would require a huge instantaneous temperature rise, it melts at about 50 kelvin but boils at over 90.
And good point about its Vietnam, cause what hes going on about during training is what was used there. Writer admits it too.
Sci-fi is, as ChrisH so rightly points out, is often used to look at current issues without having to examine them within your own time frame. Often these issues produce such fervour that it is impossible to discuss them directly. Star Trek TOS handled issues like race relations and politics which were extremely difficult topics to examine calmly in the 60s. If its locked away safely in sci-fi you might not need to scream.
I keep hitting similar items, even though Im not intending to. I think its unavoidable. Mostly though its asking the question, what if?