Scientific American has an article online called :
The article posits that the scientific evidence linking salt intake to hypertension (high blood pressure) and other ills is either weak or non-existent. As is often the case, the comment section is also worth a scan, although there are a few worth avoiding or ignoring.
We need salt to live, and like many things in life, have to have some sort of balance in how much we eat. A difficulty more common now is that many foods, especially the processed variety (and including (supposed) fresh meat) can contain high levels of salt. In effect, hidden.
Anyway, it is probably also worth reading the Wikipedia article on salt for more background.
Although one can look at salt as only Sodium Chloride (NaCl), "salt" also contains many other minerals (e.g. potassium) , and these can also be important components of a healthy diet. This might be why rock salt and sea salt have gained some popularity.