Parking Brakes w/automatics

All of mine work, none of them have ever seized or locked, and I always use them.

The pawl in the transmission that engages when you put the car in park is NOT intended to hold the car in place by itself. Not only that, but should you have a hydraulic brake failure your emergency brake could be the only way you've got to stop the car without major damage to your driveline or even the whole car if you're unable to get it stopped in a timely manner. That's why I hate it that they're called "parking" brakes now. They used to be called emergency brakes for a reason, and that's exactly why they should work and be kept in good repair.