These €50 billion is just what EDF is in debt, not what building and operating these reactors actually cost. Just in the next 10 years EDF will have in invest about €150-200 billion to replace and refurbish their reactors. That's just to keep the current capacity, not to expand it.

Unfortunately "the environmentalist movement" didn't have the information regarding the dangers of climate change and the information about the near-zero threat from low level nuclear radiation in 1970ies. Hindsight is 20/20.

That said; planning and construction of new nuclear reactors peaked in the early 1970ies, before large scale accidents (Three Mile Island and Chernobyl) really mobilized civil society against nuclear power.

The reason the West stopped building is because even with state support, it's not such a financially attractive investment. That's why "the East" continued building more and more reactors until the big incident. (Arguably their reactors were also much less safe and thus probably cheaper by quite a bit.)