Massive Curveball. This is wild. But it fits the Romulans' MO, from ENT in the 22nd Century all the way up to PIC at the turn of the 25th.
I think the Romulans are responsible for Earth's Utopia. How do I figure? I'm glad you asked.
In the Mid-21st Century, Earth was recovering from WWIII. Gigantic numbers of casualties. Societies shattered. "Nuclear winters" according to Picard in "A Matter of Time" (TNG). When Vulcan made First Contact with Earth in 2063, they were making First Contact with a planet where its inhabitants almost annihilated each other. Imagine this species joining the Interstellar Community. Imagine how much of a threat a warp-capable Earth with more weaponry would be.
In "Kir'Shara" (ENT), it's revealed that the Vulcan High Command was being run by a Romulan mole in the 22nd Century. Who knows how long there were Romulan moles in critical positions on Vulcan? If Romulans were infiltrating Vulcan even before 2063, then it's possible news of Earth breaking the warp barrier and finding out what the planet was like got back to them.
So the Romulans, who were controlling the Vulcans, made sure the Vulcans would oversee Earth for close to 100 years, to mold the planet into something more docile. Something more manageable. Something more controllable. So they called Humans savages. And Humans then spent the next century trying to prove they weren't. By having something to prove, they made themselves become peaceful, benevolent, and more diplomatic.
Eventually diplomacy fails, eventually Vulcan lost its grip on Earth, and the Earth/Romulan War finally did break out. But it was nowhere near as bad as it could've been if Earth hadn't become more civilized. 21st Century-minded Humans could've been even worse than the Klingons in the Romulans' eyes.
So I think, for its own protection in the future, Romulans pulled strings like a puppet-master to turn Earth into the "Utopia" that it eventually became.
