Parking spaces are different because an AB has no idea if one of us is looking for a parking spot while their in McDonalds eating their double big mac.
Bathrooms are a bit trickier. I mean think about it if everyone in a busy bathroom is AB there naturally forms two lines (at least in the Men's room), those who need to take a shit and those who are waiting for a urinal. If there's more than one (or especially more than two) non-HC bathroom stalls, then I feel like you're not skipping anyone in line at all. There are three lines now, one for the urinals, one for the toilets and one for the HC stall. Obviously you wouldn't skip someone else in a wheelchair, you're just not waiting in the same line as everyone else.
If there's only one toilet (like a few bathrooms at work), and someone is clearly waiting for it, I will wait in line behind them like a normal human being. I don't get to skip the line just because I roll around in a titanium exoskeleton (although a lot of the time they will let me go ahead).
But in the end it's pretty douchey when someone uses the HC stall in a completely empty bathroom because they know they are going the be there for a while taking a dump (which I guess is why they picked an empty bathroom) and want the extra 6 square feet of floor space so they don't feel so claustrophobic. Working in a hospital I run into this almost every day, I assume because 50% of people in the hospital got there at 4 am after chugging starbucks on the way and have the coffee shits every day in the mid morning...