The takeaways were that fear makes you do inhuman or dangerous things. Like when the Highlanders wanted to make the disguised Frenchman get off the boat. Those things have unintended consequences. Those things actually don’t matter at all, sometimes.

That not all heroic acts end in glory. A lot of people die in wars, tragic and mundane deaths. But they're still heroes nonetheless. George was a hero because he risked his life to help his nation's army, despite the circumstances of his death. Peter asked him "Do you know where we're going?" and George simply replies "France." He doesn't realize the severity of the situation, much less that a man traumatized by a near death experience could kill him even if he is on his own side.

The British people came to the aid of their soldiers, but it wasn't all glory and easy. That is the real purpose of the Moonstone's involvement.

Farrier is the other side of this I think. He fully knows the consequences of his actions. Not having enough fuel to return to England might mean his death or capture. But he does it to help his comrades and ultimately his nation. This stark contrast goes to show just how sad yet meaningful George’s death is.

It's funny that you say "Fear PTSD cowards" because the dad addresses George's question of "Is he a coward?" with "He's shell shocked, he's not himself, and might not ever be."