: Nylund tried to depict the Spartans as emotionally broken, not smiling or
: laughing. They'd hold their index and middle fingers to their faceplate as
: a way to simulate it, because if I remember correctly the act of smiling
: would 'open the floodgates to all sorts of emotions', if I remember correctly.

The only reason they did this was because you couldn't see through the faceplates while they were fully armored. They still smiled and joked around on their own. I think the point is that they have a harder time socializing with non-Spartans. They're basically like extreme introverts... don't really go out of their way to get to know anyone, unless they're forced into situations where they get to know them more (Cortana, Johnson, Arbiter, etc). So you'd only see that lighter side of their personality come out around people they're comfortable with.