I think most people agree that a nuclear plant can be operated safely, with a much lower environmental impact over its lifetime than a similar output "traditional" (coal/gas) power plant.
Where I think some are naive is in estimating the potential for human nature to do the things necessary to operate a nuclear plant safely for its lifetime. The problem is that most of the things required for safety (regular maintenance, proper decommissioning, technology upgrades) are high costs whose benefits do not show up immediately (or perhaps, ever) on the balance sheet. This means that no matter how well-intentioned a nuclear plant owner is at the outset, there is a chance that they will not do these things. Once an upgrade is skipped and there is no consequence, the next upgrade is even more costly, and even more likely to be skipped.
One solution to this might be more regulation, to try to force the companies to work toward goals other than the bottom line. Unfortunately, government changes over time and sometimes is clearly in the pocket of corporations rather than the public good. Assuming that you could prevent this from happening for a century or more is not realistic.
I could fault the owners of these plants for not having a perfectly spotless record of safety improvements and maintenance, or the government for failing to hold the companies to a high enough standard. But honestly, we should know better than to put our faith in any system that is inherently unstable, requires continuous inflows of money and manpower to remain safe, has an operational lifetime that spans generations, and has a large decommissioning cost.