I've never heard of a diary farmer or beef producer who decided to just let brucellosis or foot and mouth work its was through the herd hoping to achieve "herd immunity". People who say we shouldn't try to prevent people from contracting serious infectious diseases would make lousy farmers.
Yes and no, because you are suggesting there are no infections that do sweep through a flock or herd, and then immunity is achieved, plus you can try all you like to control worm infestations, and yet for as long as I've been alive all anyone can do is keep on treating for the infestation periodically, (anthelmintics excreted by farm animals being said to have a deleterious effect upon insects more widely too, a retired vet told me, and farm animals do acquire some immunity to worms as well).
In addition TB vaccine isn't used in cattle, were one available, because it might prove unpopular with the public, in case vaccine resistant strains emerge, and of course vaccinated cattle cannot be so easily identified, if they are still nonetheless carrying tuberculosis, or identified from those that do, when a vaccine isn't 100% effective.
Lousy farmers may abound, and I may have been one, but my ghon!ing on the subject of disease control is informed by many things including the views of an old lecturer called "Jaggers", who in a one hour lecture at an educational establishment that used to be called " Ewel Tech" gave me and the other students many insights.
I've mentioned a few of them on other threads, and of course I don't know what his views on this pandemic might be, but as our UK government advisory body on pandemic infection told them in 2016, infections such as Covid 19 could not be stopped in their view. All that can be done is try to reduce death rates, in the hope successful vaccines can be rolled out quick enough, so that the negative effects of lockdowns, including economic collapse, threatening our NHS more than any virus could do, saves the day, but don't assume the authorities in Sweden are advised by fools I'd suggest too.