In the modern days of health consciousness, less salt is used to cure bacon than was traditional...
It won't be be merely "common salt" (i.e. sodium chloride) when done commercially.
Of course, nitrates (and nitrites more so) are also a worry to the "health conscious". Whether they should be ... and there are fairly high levels in some vegetables, anyway. But there are a few small firms offering "nitrate free" bacon:
http://www.devonrose.com/shop/free-from-nitrate-free/nitrate-free-dry-cured-bacon.html
Both salt and refrigeration are used to inhibit bacterial action and reproduction. Because we are now told by the nannies that "salt is bad", not enough is added to cure a side of bacon to inhibit bacterial action at even low ambient temperature.
Same for smoking. There's also drying in various ways, keeping under fat (as with duck legs in France - confit), and so on. The fat would exclude the air. Something like a ham hung in a chimney would build up a blackened outer layer that would probably help to seal it a bit, besides being fairly toxic to any organism (including probably insects) that might attack the food. I guess they cut that bit off and threw it away.
You're certainly right to imply that the public health attitude to salt is not well-founded:
http://www.nutritionjrnl.com/article/PIIS0899900710002893/fulltext#sec17
Unfortunately, that's true in quite a few areas. What people have been told to do runs far ahead of what is justified by the science and in some cases actually runs contradictory to the science. The complete article that the above is from - a castigation of U.S, dietary policy by a shedload of phDs:
"Important aspects of these recommendations remain unproven, yet a dietary shift in this direction has already taken place
even as overweight/obesity and diabetes have increased. Although appealing to an evidence-based methodology, the DGAC Report demonstrates several critical weaknesses, including use of an incomplete body of relevant science; inaccurately representing, interpreting, or summarizing the literature; and drawing conclusions and/or making recommendations that do not reflect the limitations or controversies in the science ... [my italics]"
http://www.nutritionjrnl.com/article/PIIS0899900710002893/fulltext
Pushing low-fat, high-carbohydrate diets at the public when those seem likely to be part of the problem is perhaps
the major silliness. Even people like Hugh Fernley Whittingstall have climbed aboard that stupid bandwagon. But I'm going off-topic.
If you cure your own using more salt than commercial cures, then a side of bacon will be very happy in your cellar. Its cheaper too.
When you do it though, some do gooder will come along and tell you shouldn't because it doesn't fit their "one size fits all" health agenda!
As the scientists above say:
... the current sweeping recommendations for population-wide sodium restrictions that disregard uncertainties in the science and variations in individuals ...
However, really highly salted bacon, such as was made in the past, would probably taste pretty horrible. They had to use more salt, but that meant they frequently had to soak their food in fresh water to make it eatable before using it. They used to put salt cod, which was a staple in places like Portugal, in
running streams for
hours. Salted meats seem to have needed at least some soaking. There's a recipe for bacon and eggs from 1615 in Dorothy Hartley's excellent
Food in England (1954):
... cut the collops into thin slices lay them on a dish and put hot water on them, so let it stand for an howere or two. Then drain away the water clean, and pat them dry, and lay them one by one on a dish and set before the fire, so that they may toast ...
It's been seriously suggested that the large drink allowances in some monastic rules (up to a gallon of ale per man per day) were on account of the salt meat. Even after all that soaking it would probably have left you a bit thirsty.
