they kept on trying to assign him a deformity like a club foot or facial difference or hunch back- because we do assign moral value to a person's appearance and ability- beautiful people are able-bodied and cognitively normal/mentally stable morally superior and talented. Ugly people are weak crippled unable to walk due to some deformity they are cognitively deficient insane and morally bankrupt.
You ever hear of scientific racism? Phenotype traits associated with black people were seen as signs of 'disgusting' cognitive disability and lack of moral fiber. You ever hear of social darwinism? The rich are rich because they good and smart and moral and the poor deserve what they get because the are amoral stupid and bad. People cannot fathom the idea the pretty girl Lena who is socially gifted and looks normal could have a disability because she's good and normal. People cannot fathom Sarah being a mean asshole because she's so normal and has no ugly traits.
The victorian's (and let's face it us nowadays) assigned a lot of bad traits to features they found unattractive. And to many people deformities are seen as disgusting the ugliest of the ugly and physical disability is often seen as some sort of punishment. Hyde is dehumanized via people assigning disabled traits to him (even they don't fit)- because the disabled are still often seen as subhuman. Jekyll is an upstanding respectable able bodied citizen who probably has some degree of pretty privilege. Nobody would suspect the good doctor to be so vile.
Hyde isn't disabled. He doesn't have a limp. His face isn't paralyzed his nose and eyes look and work the way they are supposed to. His face looks normal possibly a lot like good ol pretty white man Jekyll's face at most he's short.
Everybody keeps trying to look for this deformity that they think will make it make sense. They think he has to be deformed or 'obviously' evil or gross in some way. People cannot fathom him being so unappealing and cruel otherwise- he has to be 'less than' them.
Its really common for us to think school shooters and other criminals must have some horrible personality disorder and to get angry at people with physical disabilities that have symptoms we find gross as something to be hidden to look at burn victims and force them to hide their scars for our comfort. People whose disabilities make it difficult to communicate (being deaf-mute, nonverbal autistic, selective mutism, speech impediments agrammartisms etc) are often told they just either need to learn to get over it or live in community specifically built for that away from the rest of the world. They are often seen as the problem because communicating gets difficult. So we assign value and negative traits to this shit- it's harder for us to deal with you so you are less not just in terms of ability but morally too. You probably deserve it even if it's out of your control and this was just how you were born.
Its uncomfortable to think that the scary pedophile criminal is a good looking dude who is mentally normal like you are. He isn't ugly or creepy he's charming and has perfect teeth. He's not wearing glasses for any reasons other than aesthetic. He's educated. He's not schizophrenic or intellectually impaired. He's not asthmatic. He's athletic. He's not some loner who never contributed to the community- he's a part of many clubs and participated in many normal social pastimes.
Its saddening and confusing to learn your sweet rich attractive friend isn't spared from being mentally or physically disabled- he can't possibly have lung cancer he doesn't smoke and is very kind. He can't have autism- he isn't bratty or humorless. Its uncomfortable to think about the fact that the reason many disabled people don't have hobbies and don't go out and participate in the community isn't because they are lazy or apathetic but because their disabilities make it too difficult and they didn't chose this.
Its easy to pathologize shitty behavior as part of a mental deficiency or disorder. Its easy to be disgusted or freaked out by a disability that causes a person to look different. Its hard to swallow that your cool best friend who did nothing wrong in life has lung cancer or liver cihroiss. Its scary to think that the good looking kind charitable man is actually a monster and that he's mentally sound. Its upsetting to think that your upper class friend who should know better struggles with all the same mental illnesses and addiction that you associate with people that are 'born on the wrong side of the tracks'
And it's scary that it's hidden not just because you can hide your problems to some extent but because
No one is ever.exemptbfrom becoming disabled - also we can hide our disabilities a lot of the time and also a lot of assholes and people who commit horrific crimes aren't mentally ill and you can't tell whose evil or a pedo or has ill intent based on appearance alone. just because they have certain physical features doesn't mean they will act a certain way.