Ive played a one armed barbarian before. He touched a cursed item that was slowly Turning him into a demon, so he chopped off his arm.

The DM said I lost Ambidexterity for that, Which I accepted. I later found out that I derailed part of his plan to make my character evil & work as a minion for the Big Bad.

It also means that people may have disabilities but won't be held back by them without removing that aspect of their life. And it could be ruled that the differently-abled aspect is something not even magic can take away because it's so intrinsic to the character

As a DM I would probably assume the player was fucking with me (because that's the mood in my friend groups)

But my response would be something like 'fine, but realize not every adventure will be wheelchair accessible, you could hardly take a wheelchair into a goblin cave. The world is not naturally kind to disabled people and this world will not be adjusted for you character'

Wrong idea of magic in my opinion. I like Tolkien's one more.

We don't play games to imagine some heavenly world where we don't need to be stronger IMHO. That'd be boring and depressing.

We play games for a world where we are stronger or know our goals in life better. IMHO again.