I completely understand your frustration, but please do not assume that all people who are handicapped either own a wheelchair or have "obvious" disabilities.
At home, my mom can get around okay (albeit with a lot of pain) due to a disease called neurofibromatosis. She has tumors all over her skin and inside her body, on her nerve endings. She is in constant pain. At home, she manages, but she has to sit down a lot and has difficulty in certain situations.
When we went to WDW during my childhood, and up until a few years ago, my mom walked right with us, and suffered, particularly once we got back to the hotel. She didn't want to drag us down. Now, she uses an ECV in the parks (she parks it outside attractions and stands in queues - we use FP and don't enter especially long ones), and she enjoys the trip so much more because she doesn't aggravate her condition. She doesn't "look" handicapped (we get many rude remarks from people when she uses her handicapped parking permit), but she suffers from a debilitating disease.
What I'm saying is, I've seen people abuse wheelchairs and I get just as angry, but please know that there are people who don't necessarily look like how you would expect a handicapped person to look
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I've definitely seen people "swap out" of rented wheelchairs, or use them to hold bags (then make a person get in the chair prior to entering a queue). It's very frustrating, it clogs up walkways unnecessarily, and it's a slap in the face to people who really need them.
