I once was in a debate with someone on a message board who said if you don't have the tag, you're not handicapped. I was telling about a client of mine when I worked home health care who used a walker and could barely get around, but didn't own a car and didn't drive, so she didn't have a handicapped sticker for when I drove her. He said, no sticker means she isn't handicapped. Like this poor woman was suddenly going to start running and skipping because she didn't have that card/sticker to hang on her mirror.
The point was, when I drove her, I NEVER used handicapped parking. There was one grocery store where the manager of the store asked me to use the LOADING zone, (not the handicapped parking which was by the entrance) to make things easier for my client and less of a hazard for other customers. The poster called me every name in the book for using a loading zone for a (in his mind) non-handicapped person.
I rarely discuss this issue anymore, and that poor, non handicapped lady passed about 10 years ago.