The Sims, at the end of the day, is a life simulator - a game that simulates life. I can understand people's perspectives on all sides of the argument, but at the end of the day, each player is going to want things for the game that others do not care about, and find unnecessary (such as Toddlers, Terrain Tools, and Ethnically-diverse Clothing and Hair), to things people will be blatantly against (Trans Sims, Cross Dressing, and Religiously-related Objects).
I agree that The Sims doesn't have to fully emulate life, there are things I don't want in my game, but we have to keep in mind that our opinions are not universal. Some people with, or without disabilities may not like the addition to the game, whether it's due to not wanting something that would make their game too 'real', don't want potential misinformation or inaccuracy in the depiction of a disability/mental illness, or feel they would do a bad job at adding it, or play the Sims to escape this part of reality etc.
On the other hand, there are people who love realism, even if it's something seen as 'grim' or 'scary', people who want to be able to tell stories that incorporate adversity on a larger scale, and people who suffer from disabilities and want to see themselves as they are.
The Sims community is diverse and full of so many different whims, and I don't envy the Gurus having to make these big decisions because you'll upset people either way, but at the end of the day, every player's wants for the game is valid, and should be taken into account (to an extent, of course).
We already have pretty controversial things in the game (not solely from my perspective, but perspective of people I've talked to, or seen comment these) such as Child Deaths, Aliens who impregnate Sims without their consent, Sabotaging, Home Wrecking, Child/Pet/Plant Neglect, Rubbish Pollution, Homelessness, Forced Schooling, Cross Dressing, Gender Identity, Traits that allude to Mental Illnesses, etc. and people continually make mods that add a lot of similar things.
At the end of the day, if they add disabilities, they're still not going to please everyone, just as if they don't add disabilities, but if they ever do, those who don't want it in their game, can just ignore it if that's what they so wish ?