In 1974 France did launch its huge nuclear reactor-building programme, dubbed the 'Plan Messmer', because:
France HAD TO DO SOMETHING about a huge energy crisis which was quickly unfolding, inducing massive strategic pressure.
Climate change triggered way (way!) less efforts.
There was NO OTHER WAY for France to reduce its dependency towards fossil fuels.
France's coal deposits were insufficient since WW1 and dwindling, hydraulic potential was insufficient, industrial solar and wind (energy) didn't exist then.
This programme was NOT MAJORLY DISRUPTING because the reactors aimed at producing more electricity: 150 TWh/year before the Messmer Plan, to 521 when it ended in 2002, they did not replace any existing equipment. Adding new equipment and developing a new sector (nuclear) is way more easy than replacing an existing one (ask Germany about coal...).
We now have to replace most fossil-fuel burning equipment.
Nuclearization plan was already running since 1957 (when a civilian reactor named "EDF1" was born, then put in service in 1963) and boosted by the "6e plan" (1971), mainly because coal reserves in France were vanishing: the 'Plan Messmer' was not started from scratch but boosted an already running one.
We now start nearly from scratch, as converting fossil-fuel burning equipment to electricity isn't easy.
France COULD to do so because this programme began when its heavy industry, stemming from post-World War II, was powerful (it now is much weaker), and in a quite rich nation at the peak of a giant economic boost.
France now fights an economic crisis and a fait part of its heavy industry capacity disappeared, even though, according to some, nuclear power saved it
Hydropower dams deployed since the 1930s and the corresponding enormous potential of suitable sites (pumped-storage dams built during the 1970s), offered a means of storing energy produced by reactors during periods of low consumption.
This potential is now considerably reduced.
Nuclear WAS JUDGED ADEQUATE, even if some leaders understood that escaping a dependency towards oil by gaining another towards uranium is stupid (they already knew France had insufficient adequate deposits, and nowadays hasn't any), because their hope was to alleviate it thanks to industrialized breeder reactors (a huge French pertinent R&D project, dubbed "Superphénix", started in 1974) or to some other trick (obtaining uranium from seawater...).
All those hopes failed flat, and even now there is no satisfying industrial breeder nor equivalent trick.
The general public (not, arguably, at least some experts) was NOT AWARE OF MOST BURDENS (accidents and exposure to terrorism/war/murder-suicides..., proliferation, hot waste disposal, dependency towards uranium providers, difficult decommission...). Even aware citizens could not do anything because France was, then, even more under heavy dirigisme and centralization than it now is (this may be difficult to believe for those who only knows its present state...).
Accident happened since the 1970's (TMI, Chernobyl, Fukushima), proliferation is patent (Iran, North-Korea...), the burden of nuclear waste isn't solved (Finland and South-Korea are the sole nations already using a theoretically adequate long-term repository and it doesn't offer an adequate storage volume. France, the U.-K. and the U.S. are waiting for theirs), France and US dependency towards Russian-controlled uranium providers, as long as decommission nightmares (the U.-K. suffers) are now clear.
This Plan may have been fueled by proponents of another plan.
The Messmer Plan neglected dismantling and waste (the theoretically relevant project, called Cigéo, is not yet finished in 2026 and even its total cost remains uncertain...), this reflects its on the fly genesis.
Some claim that this Plan has reduced the price of electricity in France, however in this matter we have to think in total cost, therefore to also consider public money expenditure: in France the taxpayer pays a large part of the electricity. By some weird fortuitous coincidence(?) the launch of the Messmer Plan (1974) marked a sharp acceleration in the increase in compulsory tax levies.
Moreover to evaluate the real cost of nuclear power we have to wait until the last waste from the last dismantled power station has cooled. Before that, additional costs (accident, stray waste, dreadful dismantling, uranium embargo, etc.) remain possible.
Nuclear power has reduced emissions from the French electrical grid. To conclude from this (even implicitly) that it remains the most suitable option after the advent of industrial renewables (wind, solar) in the 2000s is absurd. In Paris, the widespread adoption and subsequent rationalization of horse-drawn carriages around 1855 solved a significant portion of the transportation problems. Should we then deduce that it was optimal to deploy even more of them in 1910, after the advent of the automobile?