Nuclear energy should be taken seriously, then be dismissed as too expensive.

The cost of nuclear is not an inherent feature, it is a conscious choice. Choosing to make nuclear expensive, especially while allowing other, dirtier, less reliable power generation methods remain cheap, is a sign of not taking climate change seriously.

Yes, but as long as you keep research so it may become cheap in the future.

It has lots of niches where it's actually cheaper anyway. It just can't be the dominant form of energy generation.