At what point did handicapped start to mean incompetent?

Driving to work today, behind a handicapped driver, I got to thinking. People who are handicapped often have difficulties in life, so they have been given special rights such as specialized parking and entry at public buildings. These people can run the gamut from missing legs, to severe heart disease. These handicaps of these people provides them special rights over other people. That's all well and good, but at what point did getting a legal handicapped sticker and license plate give these people the right to drive like retards?

I know there are plenty of people out there who can't drive. Trust me, I lived in NJ for a while. I just recently visited FL. Scary places. But here in my home state of DE I am beset by these blue stickered psychopaths who don't seem to have much in the way of concern for anyone else on the road but themselves.

Today, behind the blue sticker of doom minivan, I watched this person do some interesting things. First and foremost, any curve, even one less than 10 degrees would involve a swerve into the oncoming traffic lane. I also got used to cycling my speed about +-20mph any time there was any change on the road. Such as shadows, sunlight, realizing there was a car oncoming, a guy way off the side of the road, a downward hill, an upward hill, and passing people sitting patiently at a stop sign. When we came to the final road I had to travel on, this person, sans turn signal, did not even bother to slow down at the stop sign and simply drove right on to the road. From what I could see, the driver didn't even glance left. Thank Christ no one was driving down that road at that time, or I would have been late to work.

This may sound like me bitching about one person, but this is just the latest blue-stickered driver that has left me cringing. Seriously, why do we let handicapped people get away with such gross negligence and incompetence? I have no solutions or suggestions or even ideas. I just don't get it.