I agree. I think the correct environmentalist position at that time wouldn't have been to oppose nuclear, but to advocate for improvements, streamlined approvals of improved designs, and public investment or incentives.

I wasn't really commenting on the merits of 20th century environmentalist movements, more raising the general point that fission power has inherent costs which weren't reflected by narrow 1950s analyses of how much energy was extractable from U-235. Operation of a fission plant requires much more capex and opex than it would if we didn't care about cleanliness (waste management), security (fissile material theft prevention), or safety (meltdown prevention).

Fusion power is more complex to invent and practically depends on modern technologies that didn't exist 50 years ago, but once the first demonstration plants are operational, marginal costs to deploy and operate more should be much lower and ultimately become very low at scale.