The brilliance of TNG’s utopia is that it is built on the premise that we had to go through a literal hell and near rural self-destruction to get to it. I don’t recall if TOS established WW3 first or not, but TNG really leans heavily into the notion that we came within inches of destroying everything.
But the moment we learned we weren’t alone in the universe, we turned it around and started building the future we could have had all along.