You know the one interesting thing about these "sane person stuck in a mental institution" stories, is they always talk about how nuts the other people were. If it were as common as suggested that normal people end up there for slips of the tongue or other mundane reasons then I'd expect there to be more "normal" people finding each other in these stories.
Probably that otherwise normal people just don't make it into the stories because they're not as memorable. Though often you'll hear of people otherwise healthy who are down on their luck, addiction problems, abuse, or just general anxiety and depression. The other problem is that the definition of sane changes depending on context.
I recall watching a documentary on Japanese school children and their attitudes towards baseball, ritualistically crying when they lost a game. A western therapist could easily justify feeding them all meds, but in reality it wasn't particularly unhealthy. I feel like a lot of ADHD is kids being kids and teachers and parents wanting an easy way to deal with it. Lobotomies used to be common less because anyone believe they cured anyone but because they rendered the patient docile. Mental health ends up being as much about societies easy function as it is about helping the patients.
I feel this comment really hits the spot on the current "epidemic" of ADHD diagnosis and prescriptions. Parents are sooooo worried about their kids not being "normal" (i.e. docile and obedient) that they will do anything to make that happen. I almost feel that it was better before we had modern medicine when parents were resigned to dealing with their kids' unique character instead of chemically forcing them into submission.
Ugh I hate this myth that "ADHD ain't real". It's a real condition that hugely impacts life outcomes. Sure there are worse diseases, and unlike other conditions ADHD people appear normal on the outside. But it makes it hugely difficult to do normal things and succeed in society. Sufferers commonly drop out of school, get worse jobs, are more likely to get involved in crime, and are less happy.
My understanding was that being trapped in an institution with crazy people, being treated like a crazy person, stripped of your dignity, and put in isolation or force-fed medication if you try to upset the status quo or challenge your incarceration in any way is enough to drive people crazy. It certainly would me.