...I wonder if it should be fine to keep brine that is full of lactobacillus and just add new veggies to old brine, not having to add so much salt (once colonized the acidity will keep fungi amd bacteria at bay, not the salt).
Even stored at 4° C, live fermented foods are still alive and fermenting. Salt slows down fermentation at any temperature.
That being said, your right salt can be reduced in many instances. It just speeds up fermentation.
I've reused brine, used brine as an inoculant in low salt brines with just a splash of vinegar added [pH 4 is good], I've wilted cut cabbage in 5% brine then washed the salt out and fermented it like that [it ferments like a hand grenade but will keep for a month at 4° C], and I've never gotten sick from my ferments.
Net salt intake is associated with a slight rise in blood pressure in some people, and a somewhat reduced vascular endothelial function in all [?] people but its instantaneous salt concentration that causes things like stomach cancer. So I avoid the super salty asian dry pickles and just keep my overall salt intake limited to healthy salted foods. Things like junk food, canned food, and chicken have loads of salt for no good reason.
...I too believe that conventional society would point the finger saying its potentially dangerous
Canned foods were invented as emergency rations. People got lazy around that time and adopted horrifically bad diets, so they latched on to canned emergency rations as staple foods. The canned and junk food market has resultantly exploded into a trillion dollar industry and controls most of the world media as well as most governments. Thats why we are all trained to be suspicious of the foods we spent half a million years evolving on.
As a kid I was perceptive enough to notice that part of every year in school was devoted to un-learning the garbage they taught us the year before. I wish every kid noticed that so theyd be prepared to question nonsense like 'milk does a body good' or that the only safe foods come in a can or plastic wrapper.