If you don't build nuclear plants, you'll get your base load generation from fossil fuels. Greenpeace has always strongly opposed nuclear power.

In itself, that doesn't mean they're wrong. But right or wrong, it's unquestionable that they have been successful at antinuclear activism. As a result, their activism has the net effect of promoting carbon pollution, and by no small measure.

As well as radiological pollution, for that matter: https://pubmed.ncbi.nlm.nih.gov/14169712/