I know that in theory it is supposed to be used to highlight issues of accessibility, but I wonder if it’s just been co-opted by the worst people in the world at this point

I mean, probably yeah, but it would be worth considering that at least part of the intent there is not just to make the obvious bad-faith claim, but also to get people to take genuine concerns over ableism less seriously than they otherwise would. I think it's often worth approaching these kinds of arguments in a similar way to which you would "I identify as an attack helicopter" memes.