That is more efficient and safer; every plane will be able to see every other, and the controllers will see the same things as the planes. No more situations where radar shows one thing and the airplane's collision-avoidance system show another.
The down side is that the signals aren't encrypted, so anybody can listen in. On top of that, using a software-defined radio (basically a radio whose characteristics are determined with a small computer rather than the usual hardware), it's possible to transmit the signals that a plane does to the tower, and there would be no way to tell. A good radio can be had for about $1,000 or less.
It's easy to see why this could be a problem. While a hacker can't take a plane from the sky, he or she could certainly cause a lot of chaos at the airport by simply filling the air traffic controller's screen with a lot of fake airplanes. Even though each aircraft could be checked against a flight plan it would still be difficult -– if not impossible - to do.
They wouldn't be completely helpless, of course, and even if the planes were getting confusing signals from the ground, visual and radar cues would prevent a lot of accidents. (So if you're thinking of the plot to "Die Hard 2" you can relax). But a major airport forced to shut down for even an hour would be a major headache.