Fossil fuel companies opposing it I can understand: it’s a straightforward, strategic move.

For green proponents, I think it was an own goal, likely driven by a mix of fear and failing to realize that people would not readily temper their demand for energy and the holistic solution needs to include humanity harnessing substantial amounts of energy. Ruling out nuclear directly (in a single step) means decades of people creating gigatons more emissions from burning fossil fuels.

After all, nuclear power was brand new. And the pollution and death if one goes bad...