How exactly does an opposition party force the country to do something like this? Why is it the fault of the Green party, and not of the parties that were in government at the time and made the decision?
That is incredibly biased framing. The main opinion in the broad population at the time was that nuclear power was too dangerous. You're right that the governing parties followed this to stay in power, but how is that then the fault of the opposition party, not of the governing parties?
The green party wasn't able to make this happen or not happen, as they had no governing power. The governing parties were able to make this happen or not happen. They chose to adopt part of the opposition policy to gain political power, but doing this also means they have to accept the responsibility for those decisions.
They might not having governing power, but these opposition parties, as well as NGOs like Greenpeace had a lot of propaganda power that they used for evil.
Even if this were true (and I strongly disagree with both the idea and the framing), it would make the governing parties complicit in the "evil". They could have used their power to fight against the "evil", but instead chose to participate in it to score political points.