Kirk might also be quoting an old slogan, one grossly outdated by historical developments now, but at least as closely associated with the RNZ as the phrase "peace in our time" is with WWII.
You said that "Stiles' distrust of Spock and his entire species is a very rational concern" Are you crazy?
Perhaps. But I do maintain that the evidence was very much in favor of a species-wide conspiracy, from a species known to have fought a species-wide war against the entire mankind - probably one aiming at annihilation and lacking in mercy and other niceness, judging both by the briefing scene dialogue and by the later evidence of the Romulan xenophobia. Our heroes ran into Space Nazis here, and were belatedly awakened to the fact that people in their midst had been wearing the uniforms, boots and swastikas all the time - every man, woman and child of them. Stiles' concerns would be about as racist or counterfactual or falsely generalizing as the claim "all blacks have skin colors in shades of brown". What practical significance the claims would have would remain to be seen.
Sometimes it seems like you type these long ass explanations and happen to just throw in some crazy stuff to see if anyone is paying attention.
I just happen to wonder if people really are as stuck with their assumptions as they appear to be, when the fantastic science fiction context really flies in the face of just about any assumption we dare make.