The reason so many people illegally park in handicapped spots is that they know most people are too cowardly to call them out.
Most handicap spots I see are EMPTY. I think truly handicapped people should get the privilege of minimizing their effort to get from car to store, but I also think its a lot of wasted empty space most of the time. Regardless, I don’t go scouting the parking lot for cars parked in a handicap spot that don’t have a handicapped placard. Go for it if you want to put yourself out there, but its not a civic duty, and it might be a good way to wind up in a confrontation you will regret later.