…And BTW, people with adeno- and tonsillectomies seem to have increased risk of obesity and of heart-attacks, among others – hmmm.
Around 1900, America started to have frequent polio epidemics. Starting in 1916, they happened every summer, which came to be called "polio season". Over the years, they got worse. In 1951, thousands of children died, and tens of thousands were crippled. … As both tonsillectomies and polio increased, a horrifying correlation emerged: Children who'd had a tonsillectomy were more likely to get a certain type of polio (infection of the bulbar region of the brain stem) than children who had not had a tonsillectomy. This became common knowledge. Polio Pointers said "don't have mouth or throat operations during a polio outbreak." In 1954, the American Journal of Public Health ran an editorial summarizing the link between tonsillectomy and polio. The main evidence was that within a group of children with polio, the ones with bulbar polio were about three times more likely to have had their tonsils removed than the ones with spinal polio (infection of the spinal cord). This resembles some of the first evidence connecting smoking and lung cancer: Hospital patients with lung cancer were much more likely to be heavy smokers than hospital patients with other diseases. Although Polio Pointers implied that tonsillectomies were unsafe only "during a polio outbreak," this was false. The data implied they were always unsafe: "This higher proportion of bulbar cases in tonsillectomized persons occurs at all ages regardless of the time elapsed since operation," said the editorial. A 1957 paper about the tonsillectomy/polio association cited 19 studies that had observed it. "The association is generally regarded as an underlying causal relationship," said the paper, meaning that the usual explanation was that tonsillectomy increased risk of bulbar polio. The paper found more evidence for this explanation. Researchers considered other explanations for the polio/tonsillectomy association (for example, are tonsillectomies more common among rich children? among sickly children? ) but failed to find supporting evidence. The tonsillectomy/polio connection is probably why tonsillectomies became less popular starting in the 1950s. They declined from extremely common (the most common of any operation) to very common (the most common operation done on children).
By 1960, the tonsillectomy/polio association was firmly established, but its explanation was a mystery. If it reflected cause and effect, why would tonsils protect against infection? Around this time, work by James Gowans and others started to answer this question by figuring out that lymphocytes are the main cells of our immune system. They detect bacteria and viruses and make antibodies against them. T cells, B cells, and natural killer (NK) cells -- all lymphocytes. In one experiment, Gowans and his co-workers drained the lymphocytes from rats. The rats lost the ability to make antibodies. When the researchers put the lymphocytes back into the rats, they regained the ability to make antibodies. That's just an example. Our understanding of what lymphocytes do comes from thousands of experiments.
When the function of lymphocytes became clear, the lymphatic system made much more sense. Lymph washes germs out of tissue and into lymph nodes, where lymphocytes detect and try to kill them. The high density of lymphocytes in the nodes ensures that germs will bump into them and be detected. When lymphocytes detect more germs than usual, they multiply and the nodes enlarge. Tonsils … like lymph nodes are full of lymphocytes. Their shape and placement causes them to sample the bacteria in your mouth, so they protect you against the bacteria in your mouth. Tonsils become swollen and sore during infections because the number of lymphocytes inside has increased -- the lymphocytes are fighting off the infection. These facts about the immune system and the lymphatic system, including the function of lymphocytes, are part of high school biology. …
Removal of your tonsils is removal of part of your immune system. Our understanding of the immune system implies that removal of tonsils reduces ability to fight off infection. We cannot say exactly what tonsils do, just as we cannot say exactly what many parts of the brain do, but our general understanding of the immune system (based on thousands of experiments) implies that removal of any part of it is very dangerous, just as our general understanding of the brain (based on thousands of experiments) implies that removal of any part of it is very dangerous. When a child gets a sore throat, it suggests that his immune system is not doing a good job fighting off infections; a better-functioning system would have killed the germs sooner. Cutting off part of the body that fights infections because of too many infections makes as much sense as getting rid of fire houses because of too many fires. If your outcome measure is narrow, you may conclude that damaging a vital organ is beneficial. For example, prefrontal lobotomies were once claimed to be a a good thing (some people became less disruptive). In rare cases, the benefits of removing part of a vital organ may outweigh the risks. If I were in intractable pain, I might agree to have part of my brain removed. But not because of six sore throats.
If you search tonsillectomy/adverse effects on PubMed, you will get more than 1000 references. There is no sign in the [Cochrane] review that the authors did that search or any other search for bad effects of tonsillectomies. If the authors had looked at the PubMed articles published before their review (about 900), they would have learned that the risks of tonsillectomy include polio, weight gain, vomiting (many articles), taste distortion (here, here, here), Hodgkin's disease (here, here, here, here, here, but here is evidence that disputes the association), Creutzfeld-Jacob disease (e.g., here, here), inflammatory bowel disease and Crohn's disease, rheumatoid arthritis, severe spine infection, neck infection (here, here), speech problems (here, here), hearing loss, ear pain, visual loss (here, here), depression, several other serious problems, and immunological abnormalities (e.g., here, here, here). They would have learned that tonsillectomy "is associated with a relatively high risk of postoperative complications" and that "the actual post-tonsillectomy haemorrhage rate is much higher than that recorded in hospital statistics." (The Cochrane Review says this risk is "small".) They would have learned, if they didn't already know, that "the tonsils have a large immune function."