My main takeaway from this episode was the Romulans and Vulcans being the same and what the implications on that for Starfleet and Spock especially.

Romulans are like Vulcans? Does that make Vulcans bad? Romulans good? Spock is already the different one on the bridge? Will the rest of the crew believe in Starfleet ideals or will they turn on Spock and allow racism to rule the day.

Tie this to treatment of Japanese civilians in the US during world war 2 (something Sulu's actor was unfortunately quite familiar with). Are all members of a race bad because the governments are at war? Obviously not but this is a common refrain from the ignorant and afraid during conflicts.

Ultimately the Enterprise and the Romulan captain stop seeing themselves in terms of soldiers fighting for their side and instead as 2 people caught in the middle of the fight between their governments. The Romulan captain's sacrifice in the end exemplifies the realization. Rather than continue the conflict and drag both sides into a brutal patriotic conflict, he sees the humanitarian cost of such a conflict and therefore, the intrinsic value of life of both sides.

The episode wants to drive hope the point that people are people, no matter nationality or political conflict. At the end of the day we are all the same. Despite Stiles racism toward Spock, Kirk and by extension the Federation-idealized humanity, will have none of it.