> many people are used to floods caused by heavy rain, and the danger feels similar.

I don't know what "people feel", but the reality of a large dam that is blown up is more like a tsunami than a normal flood. If it hits a city, casualties can easily reach the 10s or 100s of thousands, instantly.

In a way, an upstream dam is a health hazard for anyone in the area that might be flooded that should be concerning at the same level as living in an area that has had some nuclear contamination.