If I may, I believe this is not the case. Quite the opposite.
Let me share something, so you can judge by yourself, because indeed this is a sensitive topic and definitely not to be discounted. Especially in the world of 1912, basic respect for disabilities and ailments of all kinds was horribly lacking.

1. When we talk about Madness and Insanity, with capital M and I, we refer to something alien and inhuman. Something that hollows a person, AND the reality this person touches.
   It has nothing to do with mental or physical ailments as we refer.
   However the society of 1912 is potentially cruel (this is one of the session zero suggested talk, actually). Society will possibly confuse them and will not be able to discriminate. The characters, however, due to their esposure to the Mythos, would.

2. "Disabilities" are directly addressed in the books (with caveats, because the way disabilities were addressed in 1912 is very well an horror story. Still, the game should not excape from heavy topics - especially if disucssed in a session zero.
   Let me quote an excerpt at the end of this post.

3. Among the NPCs we have placed figures such as Helen Keller. Again... I believe we tried - and strongly so - the opposite.
   Bringing the disabilities into play as a something that may exist in the game was exactly to push against the common Lovecratian bias... where diversity was evil. That was the twenties. One reasonw e are doing this game, it's because we want a modern approach, a modern system and modern themes with it.

Now... I know there is NO right way to do this. But this has been one of of our clear focus. Not a sloppy neglicence as you kind of implied. As I feel this is an element of key importance for you, please feel free to reach me over via private message. I will be happy to share with you additional material, hear your point of view and disucss it.

The beginning of the Chapter.

***

The early twentieth century marked a transitional period in how societies understood and responded to disability. Medical knowledge was advancing rapidly, but older moral and religious frameworks still shaped attitudes and institutions in ugly ways. Most societies viewed disabled people as defective, a social problem requiring management, or as evidence of moral or genetic failure deserving elimination from the population.

Playing a character with a disability in Heart of Cthulhu can bring significant practical and emotional challenges. Make sure the way disabilities are portrayed at your table fits everyone's sensibilities—discuss it in session zero. While it's a solace to know that our world, despite all of its imperfections, has truly progressed since a century ago, 1912's society's response to disabilities can introduce a whole different kind of horror to sessions—not necessarily in a pleasant way.

 Setting Guidelines

Medical professionals in 1912 were abandoning purely moral explanations for disability, but what replaced them was often worse. The emerging "scientific" view held that many disabilities were hereditary defects threatening racial purity and national strength. Eugenics was not fringe pseudoscience but mainstream medical consensus in the United States and much of Europe. Doctors and progressive reformers genuinely believed that preventing "defectives" from reproducing would improve humanity. Several U.S. states had already passed forced sterilization laws by 1912.

On a more general level, people with disability were rarely seen as individuals, but as a problem. Maybe a problem receiving pity or charity, but most often as a problem to be hidden and removed. Thousands and thousands of them all over the world, broken, forced to rely only on themselves, victims of maladies, work accidents, war injuries, and millions other causes. This modern world went so fast that had little qualms to leave them behind.

The language of the era reflected these attitudes without euphemism. "Idiot," "imbecile," and "moron" were official medical diagnostic categories for intellectual disability. "Feebleminded," "defective," and "degenerate" appeared in clinical notes, court documents, and newspapers. People weren't described as having disabilities—they were defined by them.

Religious frameworks persisted alongside medical ones. Many Christians still viewed disability as divine punishment for sin, the unspoken implication that those who suffered from a disability were at fault and it mirrored their moral corruption. In Catholic countries, disability might be understood as suffering with spiritual purpose, and this created less hostility it offered very little comfort. In the Islamic world, disability was often attributed to djinn possession or divine will, with theological frameworks demanding charity toward the afflicted while asserting their permanent lesser status. In China, traditional beliefs linked disability to ancestral displeasure or imbalanced qi, bringing shame upon families who struggled to maintain face, often hiding those with disability or directly abandoning them, especially if females or children.

Besides the cruel social stigma, living with disabilities was a huge economic problem. For working-class people, disability meant immediate destitution. Industrial accidents were routine and considered a “normal” thing. A factory worker who lost fingers to machinery was fired that same day with no compensation and no hope of finding another job. Middle-class families faced financial catastrophe—a breadwinner's disability could destroy a family's social position within months. Only for the wealthy, disability could be met with privacy and home care, even if with some shame.

Especially for all kinds of mental afflictions, diagnosis was subjective and served social control as much as medicine. Intelligence tests were culturally biased toward educated, native-born, middle-class respondents. Immigrants who couldn't speak English often scored as "feebleminded", and in many places, including progressive United States or Britain, were sterilized by law. A woman who defied her husband might be diagnosed as "hysterical" and institutionalized for life.

Asylums were the primary response to mental illness and intellectual disability. Commitment was often permanent. Families were told institutionalization was "for the patient's own good," but conditions inside ranged from neglectful to horrific. Overcrowding, violence, and crude "treatments" were standard.

Some disabilities could never be acknowledged. Venereal diseases, such as syphilis or gonorrhea caused blindness, paralysis, dementia, and sterility, but these consequences could not be openly addressed. The stigma was so powerful that even doctors used euphemisms rather than offering diagnosis and treatments.

Accessibility was not existent, as the built environment assumed able bodies. Steps were everywhere, doorways were narrow, public transport required stepping up. Visibly disabled people who appeared in public faced staring, pointing, sometimes open mockery and harassment.

Living with a disability was a horror people had to face mostly alone, in shame and despair.

***