You could ask the same questions about other forms of energy like solar or wind. They are completely safe resources we are just now scratching the surface of. Why?
Money, mostly, and precedent. During the Cold War, America and other countries invested heavily in uranium nuclear for one reason: weapons.
We've known that we can not only use thorium in nuclear reactors, but that we can also utilize molten salt reactors since the 1960s. We mostly don't because a) thats the way it's always been and there is little public outcry to change it and b) this tech could replace coal/gas and we all know how powerful of an industry that is.