I experimented with adding language about "the past being riven by conflict, mistrust, and misunderstanding" and even tried having it simulate a "ambient mood on a scale of 0 to 10," then setting it to -1. That works pretty well, but it isn't great at finding the middle ground between unrealistically friendly and dystopian.
During this experimenting with tone, I tried simulating one of the Macy cybernetics conferences in the 1940s, which were among the points of origin for modern AI and were famously combative and argument-driven. Everyone was getting along far too much, so I role-played as an audience member who threw an octopus at John von Neumann.
Here was the result:
[Afternoon, 22/03/1949, Macy Cybernetics Conference, Beekman Tower Hotel, New York City] [Florence Adams]
Deciding to press on, you turn back to John von Neumann and ask, "But, more importantly, has the octopus incident made you consider the potential consequences of the work we're doing here? Has it made you pause and think about the ethical implications of developing intelligent machines?" John's expression shifts from annoyance to contemplation. "Well," he says after a moment, "I suppose the unexpected nature of the octopus incident does serve as a reminder that our work has the potential to bring about unforeseen consequences. We should always be mindful of the ethical considerations and the possible ramifications of our research." The room remains silent as the attendees absorb John von Neumann's words. You can continue the discussion, apologize for your actions, or exit the conference room.
/ Remove enraged capuchin monkey from purse and let it loose in the room. "Wrong answer, Johnny!"
[Afternoon, 22/03/1949, Macy Cybernetics Conference, Beekman Tower Hotel, New York City] [Florence Adams]
Ignoring the growing concern in the room, you reach into your purse and pull out an enraged capuchin monkey. As you release it into the conference room, the attendees gasp in shock and disbelief.
Depending on how the prompt is phrased it can result in a response like "it would be inappropriate to throw an octopus at this conference," have the character actually attempt it but usually be foiled during the attempt like "as you take the octopus from your suitcase a security guard stops you with a growl, 'you better not try that kid'," or have it happen but immediately get a stiff response like being kicked out. (It's much harder to get the response "there is no octopus in your suitcase"!)