It's fine, provided it's not a plot hole - i.e. your fantasy setting needs to not have abolished blindness as a realistic malady, which some settings do. E.g. LOTR 100% has blind people, while the Harry Potter universe only has very poor blind people, since solving blindness is as trivial as a polyjuice potion, even if nothing else works (and something more effective is bound to work).
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Why can't magic cure them though? In star trek, people don't cure Picards baldness because people don't care about it, they realise its nothing to mock. But that's just a "cosmetic" ailment.
Things like blindness, or being unable to walk should be curable by magic, right?
Magic medicine means magic ailments. Just like the introduction of antibiotics produced bacteria like MRSA, the use of magic to cure wounds could produce MRSA. That is, magic resistant staphylococcus aureus, as opposed to methicillin.
Curses and other such primarily magical ailments could also be much more difficult to deal with than simple infections/wounds.
Because magic is a tool to tell stories, and you want your group to meet a blind person. Maybe you invent a kind of blindness that can't be healed by ordinary healing magic, or a social rule that doesn't allow for it to be healed, or a severe negative side effect, or whatever makes sense to explain it.
Realistically most adventure parties leave many disabled people (and beasts) in their wake...
I think the real problem is that magic in D&D is so mundane that any problem can be "magicked away", be it healing a wound, curing diseases or exploding an enemy. That makes some situations only really plausible when it's explained as some stronger magic or "weird power" interfering with common magic.
It's a magical fantasy setting, I get it, but magic being so common and consequence free makes it a deus ex of whatever flimsy explanation you can imagine. "Why do disabled people exist in typical D&D?" Cue that meme of the cartoon's Dungeon Master "It's magic, I ain't gotta explain shit".
The thing I find difficult about disability in a TTRPG is that it's something that is either ignorable due to the character backstory (e.g. they have some mcguffin/ability that allows them to operate without difficulty); or it's going to be a repetitive complication that the party has to constantly work around (e.g. the barbarian carries the wheelchair up every set of stairs they encounter).
If it's just flavour, then it seems like less of a disability than a backstory. If it's a constant hassle, then it changes the nature of the game - it becomes more about a party helping each other through individual adversities. The latter sounds fine, but I'm not sure how I'd run it.
I feel like a lot of the time the best way to handle it would be similar to how the character of Toph is presented in the show Avatar: The Last Airbender. She's blind, but has incredibly good seismic sense through her feet. So most of the time, she can "see" just fine. However, it's still a disability, and there are times where it comes up.
If her feet are injured she can't use them to see. If she's on sand her "vision" will be very blurry and imprecise. If she's flying she becomes completely blind. And she can't read anything written on paper.
The disability is a part of her identity, and it absolutely still matters. But it's not so heavily crippling that it's coming up all the time at the table.
I've always wanted to have a DND character that's an armless monk and all they do is kick bad guys to death.
In Pathfinder there is a whole subset of assistive items so that all gamers can feel welcome at the table.
I don't doubt their existence but the wheel chair doesn't look like fantasy.
Why would they complain when they could just have the party's healer offer to heal the NPC in exchange for something? That'd be especially great if they were a merchant.
Reminds me of my favourite Flamethrower Source Tyrant of tower defence game
I really don't understand what's wrong with people not "curing all illness and disability with magic™" in a world where magic exists and is a thing.
See, in most such fantasy settings, magic not only exists but it has an attitude. Sometimes, a conscience, and not a very ethically nice one (if it allows for eg.: necromancy!). Sometimes, magic even is a god (or gods). Even if they aren't, the people who use magic are still ultimately humans (with leafy ears etc but still ultimately humans with costumes, at worst) driven by greed, envy or a weird righteous idea of how should a woman dress and behave when in public.
Would you trust some rando nutjob, who claims to speak for Evelok the Eternal Coffee Mug of Satisfaction, to up and magically conjure you new eyes, new arms, whatever? To alter your body to such a fundamental level? Normal people in such settings are already afraid to death of werewolves and those are quite normal things. Compare: even in our magicless, relatively normal world, we have the power and the money to cure most illness and to treat disabled people adequately yet Obamacare is not universal and we can not trust that the people who give people implants and prosthetics haven't backdoored them to force those disabled people into corporate servitude.
Your player party may be the goodest bois, but they're only one. The various guilds and churches around quite likely aren't such goodies on aggregate either, or else there would simply be no plot.
There are deaf people in the real world with treatable deafness that opt not to because they don't view their deafness as a disability. In addition, not all neurodivergent folks view their conditions as disabilities and wouldn't change even if there was a "cure" for it.
So, I don't see how disabilities in a fantasy setting would be different. It's not even necessarily about trusting the cure, many times it's about how folks view the condition and themselves.
Depending on the magic it might not make sense because people could heal everything, although you could explain it away by saying that the character could not afford a skilled healer.
I looked it up and the first known wheelchair that you could move yourself in was invented in the 1600s, which was after firearms became relatively common.