I have a blue badge. I have really serious post-chemo fatigue (sometimes, I literally can't move after a day of fairly mild activity) and also something called peripheral neuropathy - nerve damage in my feet. But I use the blue badge very sparingly because I'm aware people do challenge, and I don't have the emotional resilience for it (am dealing with my son's EHCP right now as well as the fallout of cancer). I need a wheelchair to go to a shopping centre, and right now my feet are burning just from moving around the house today - I've not had the energy to go out. But if I pop to a cafe, with no long walk (thanks to the blue badge!) I do walk from car to seat, because actually one of the only ways to overcome chemo fatigue is with gentle, small bite, incremental exercise. So I need the blue badge to access the level of activity I need to not need the blue badge (my very much hoped for end point!) and yet I am sometimes too drained to use it, in case I get hassled. It's a real issue. And before all this, I was a fairly assertive person. I had the energy to be.
If I ever am challenged, I plan to tell them I have cancer and then show them the port-a-cath on my chest where I get intravenous drugs administered. That should hopefully shame them enough to actually listen when I explain about invisible disabilities, and that just because someone has the use of their limbs, it doesn't mean movement is easy.
My son would also be entitled under the new rules, as he's ASD and while able to move physically, he's pretty agoraphobic because he finds the world threatening and overwhelming. Being able to park closer to a destination could really help reduce his stress levels. I'm having to weigh up the benefits (his activities are restricted by his getting so overwhelmed by noise, crowds and bustle) versus what it could do to his anxiety levels if someone were to aggressively challenge his right to have that extra help. It would without question harm him, and reduce his willingness to go out even more.
I wish people would understand that not only is it not their business, they can take emotional energy from people who, by definition, do not have much to spare. In cases such as my son's, they could exacerbate the effects of a disability in a very direct way.