I'm not against nuclear but I don't think we had it solved then. To really advance, we need plans that provide for exponentially more energy production cheaply and reliably. We're talking about renewable projects that produce megawatts and low gigawatts when we need to be thinking about how to someday produce Terawatts and Petawatts. It's those kind of energy sources that will help us move forward as a species. If we could get to virtually free clean energy, then problems like fresh water go away--desalinization becomes cheap. We could position ourselves to harness new sources of raw materials like asteroids. Etc.
Also, the space capitalists like Elon Musk are kind of crazy, but they aren't wrong that someday we need to be moving toward a future where we get off this rock and find a way (at least over millenia) to move beyond our solar system, if we want humanity to have a really long term future. A future built entirely on economizing and reducing energy usage doesn't get us there, especially if it pushes us back a couple of generations in tech usage. Efficiency is fine, and we need to address climate change short term, but ultimately we need to keep an eye on how we level up.
It's maybe a harsh way to look at it, but it's possible that if we're not growing, we're decaying.