The public perception of the dangers of anything radioactive is quite exaggerated, the politicians in these cases are only representing the views of their constituents. Having said that, I don't think you can reduce the argument to something as simple as salt in an ocean. Like you (almost) said, the concentrations are extremely different, particularly if something goes wrong with the containers in the millennia they are buried for.
http://xkcd.com/radiation/
Not entirely related, but an interesting read: http://en.wikipedia.org/wiki/Goi%C3%A2nia_accident