For those ignoramuses among us here, disability also can be variable.
Disability doesn't mean using a wheelchair, although it can.
It can vary from poor balance, neuro-fatigue, pain, breathlessness or struggle walking if the distance is too far.
On a personal note, I have Multiple Sclerosis, which although is degenerative, is also variable from minute to minute, not just day to day.
I start the day with 40% battery charged, whereas everyone else has 100% batteries charged.
A shopping trip might take 10% of my batteries one day, or only 5% the next. What those idiots might not understand is this: that once battery power is spent, it's gone for the rest of the day. So you have to choose wisely what to spend it on.
Some days even getting dressed and breakfast drains 20%. On a day like that, all symptoms are so aggressive that I can't even think about leaving the house.
On a "good day" (which by the way isn't even close to being a bad day for a normal person), I can manage a trip to the shops. But the effort of getting round the shop and driving back home, drains a huge amount of battery life and so I have learned to utilise all the resources available to me, in order to pace myself better.
A blue badge is just one way of achieving that.
If you looked at me, you would not know I am feeling sick with tiredness, finding it hard to focus on the task at hand, having to concentrate hard on balancing so I don't fall over, feeling numb on one side, starting to talk with slurred speech, feeling desperate to lie down somewhere.
All of those symptoms (and more besides) qualify me to use a blue badge. One day I might need a wheelchair, as a lot of people with MS have to. But for the moment I can get by without. It doesn't make me any less disabled though. In fact, one friend with MS told me she was much less disabled now that she has a wheelchair, because she no longer has to work as hard with balance and fatigue with walking, and that sort of thing.
OP. some people just can't imagine beyond their limited experience. Feel sorry for them! It can't be nice to live in such a narrow view of the world.
But in answer to your post, YANBU. Absolutely not.