Nutrition professor Marion Nestle argues that we should lower our salt intake, and that studies showing no correlation between high salt intake and poor health outcomes only fail to do so because finding a low-salt-intake control group is now almost impossible.
For her, the two main culprits are processed food and restaurant food.
The latter isn't surprising; in culinary school one of the cardinal sins they hammer into your head is to never send out a dish that is under-salted. Salt enhances flavors of a dish. At a poor low-end restaurant, most dishes tend to be too bland or under-salted. At a higher end restaurant, it's more often the case that a dish comes out over-salted because the chefs there err on the high side.