The fairly obvious point is that the only thing which should...

The fairly obvious point is that the only thing which should matter when it comes to energy policy are these factors (in order of importance):

- Reliability
- National Security
- Cost
- Impact on environment

Energy is useless if it does not work 100% of the time, enable free citizens to do whatever they want to do in terms of energy consumption (run air conditioning / heating etc) and must also provide some sort of capacity management whereby peaks in consumption are are also able to be met with supply.

National Security is obviously at the top of the list of importance given most rationale human beings prefer it when their governments are able to defend their own borders. See Europe's mess now that half of Europe is reliant on gas from a country that hates them.

Cost is key because unaffordable energy disproportionately ruins the lower class and people who can least afford it

Finally - once the above three points are satisfied then I agree environmental considerations should be considered and as much as possible, the sources with the lease impact on the environment should be used (but only if the first three points are satisfied).