I spent 5 years using a wheelchair before finally getting enough pain relief to walk again. I still "confront" people about this. Usually it's a quick "hey, that's a hc spot." I've also been confronted, and harassed. Here's my take. If someone has a tag, I let them be. If not, I point out that they are in a hc spot and let their response dictate the conversation from there. People doing this to me never bothered me. What is a problem is when someone decides that a person with a tag doesn't deserve one. Unless you are a doctor, stay out of that one.
As for people who feel it doesn't effect them. Maybe not now, but you never know. I went from being an athlete to disabled in a short period of time in high school, so age wasn't a factor. Finally, you (generic) may only be there for a minute, but in the meantime I looked from the road, saw all the spots full, and decided I would do without whatever I was going to buy at the store. And to member this is exactly the same as racism and homophobia.