I think that some people "need" this. Most don't. The problem is, how do you draw a line...? You can't. That's why all disabled guests, no matter how capable of standing in a queue, get the privilege of queue jumping.
The problem is, people do abuse it. And, honestly, how many people wouldn't abuse it if given the option to?
I don't know what the solution is. There probably isn't one. Maybe something less blatantly in the face of queuers who could potentially have been waiting hours, would be nice. Such as a fast-pass system in which guests HAVE to ride at designated times. Or, better still, guests who are still able to stand in a queue should only have the privilege of fast passes. I do find it slightly annoying that people perfectly capable of standing should get to jump the queue.
And the "well, the rest of their lives aren't as great so it's nice to give them something to make it better" doesn't fly with me. We all have problems. And I do not think mental or physical ability in any way determines ones happiness. By this logic, we should let those diagnosed with depression not only queue jump, but we should give them free ice creams all day too.
the issue is in drawing the line on who is and is not legible.
EDIT: It's annoyed me that in this topic people have gone "this is silly, I have ADHD! It doesn't affect my ability to stand in a queue!" as if everyone experiences it the same. Also, the above poster mentioned autism. Again, not all autistics are the same. There are infinite degrees of any mental or physical disability. It's not black and white.