The anti-nuclear stuff seems to pair up quite well with "you need to start importing a lot of natural gas", which makes me think it is simply an agenda pushed by a certain rather large country to the east.

You don't have to wonder, because it is the agenda that you're thinking about and also the agenda of fossil fuel companies.

But we now have two lessons that teach us that being anti-nuclear was stupid: the Ukraine war and the current US administration's adventure in the Gulf.

This is now. But the seeds were sown much earlier.

The west, you mean?

The anti-nuclear area, at least in Western Europe, had historically a very high correlation with those who held sympathies for a certain very large nuclear power who would have strategically benefited from an anti-nuke sentiment that would avoid another nuclear power's weapon deployment in EU bases. But I'm sure it is a coincidence.