The left wants to use environmental worry to control the population

Justin Haskins:

Why the Environmental Left Is Secretly Petrified by Truly Renewable Energy

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As Fox News noted in a recent report on the potential discovery, "[n]uclear fusion is the be-all and end-all source of energy because, in theory, it's practically unlimited and has almost no downside. It doesn't put carbon into the atmosphere like the burning of fossil fuels or generate radioactive waste like nuclear fission, which is the technology in current nuclear power plants."

If nuclear fusion is achieved, it will in relatively short order render much of the existing energy market useless. Many traditional power plants would close. Carbon dioxide emissions would be cut dramatically in countries with enough wealth to build nuclear fusion plants. Billions of people would have access to affordable energy that they never had before.

This scenario might sound as though it's every environmentalist's paradise, but there's more to leftist environmentalism than obsessing about global warming. For many on the left, growing human population sizes and their effect on the environmental is also a very serious concern. For instance, in his population control book Ten Billion, environmentalist Stephen Emmott wrote, "Only an idiot would deny that there is a limit to how many people our Earth can support. The question is, is it seven billion (our current population), 10 billion or 28 billion? I think we've already gone past it. Well past it."

University of Hawaii at Manoa professor Camilo Mora wrote in a 2014 paper in the journal Ecology and Society, "What caught my interest on this whole issue is how humans are causing the destruction of ecosystems. At the end of the day ... we cannot stop hurting biodiversity if we don't stop reproducing so quickly."
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The left has been worried about the "population bomb" for centuries.  They seem to constantly underestimate the creativity of human science in producing food and dealing with growth.