Way less dangerous that a lot of other things on our planet. Fly ash has a use in concrete and concrete products. Bottom/economizer ash has uses as a road base. Coal burning utilities don't shut down because of ash. They shut down due to over regulation.
Years ago our local town decided to repave all the streets using coal ash as a base. It worked great until some old biddy got a summer cold and blamed it on the ash.
The project was shut down and there are still unpaved streets around here because of HER.
My driveway has bottom ash in it, and I used lots of it to fill holes where there used to be an orchard.
I often used cement mixed with only bottom ash for various light concrete projects. After almost thirty five years some are still holding up.