I don't want to be here in 30 years time wishing we'd built reactors 30 years ago (which is where we are today)
The current situation where you might regret not having built more reactors 30 years ago is not comparable. Renewables were not competitive with nuclear 30 years ago. But that situation no longer obtains.
Eventually, all fossil fuel use must be replaced, but that has nothing to do with the issue of responding to Putin that I was addressing. And the backup generation can eventually be non-fossil also, particularly hydrogen. Europe has massive amounts of potential capacity for underground storage for hydrogen, far more than would be needed.