I agree that most of the time people should cast disabled actors for disabled characters.

However I also think that for something as extreme as ALS, where someone swiftly loses the ability to move any muscle except their eyes, it's very difficult to cast a person with ALS to play that role.

It's a very fair claim to say "someone with a wheelchair at least should have played Stephen Hawking even if they didn't have ALS per se".

But expecting someone with ALS to play Stephen Hawking would be extremely difficult because if they weren't already at the advanced stage of paralysis that Hawking ended up living in for decades (where he could only move a few muscles of his face) the progression of ALS is unstoppable and unpredictable, and it's very unlikely that it would follow the schedule of a film's production. If someone with ALS was cast at an earlier stage of the disease, by the time it came to the actual filming they might be completely paralyzed and be unable to do the earlier parts of Stephen Hawking's story.

Most people with ALS die after a couple of years of being diagnosed. Hawking was an extreme outlier in ALS in that he's thought to have lived decades longer with the disease than anyone else with ALS.

Let alone trying to find someone with ALS who has the acting training and physical resemblance to young Hawking that Eddie Redmayne had.

So I think while in general people with disabilities should be cast as disabled characters, I also think that it is nuanced in that they don't need to necessarily have the exact same disability as the character. Perhaps someone with paraplegia or cerebral palsy could be cast as someone with ALS for example.

Curious to hear your thoughts on that.