In the movie there are 3 laws that the robot has to follow. One robot who is turns out is given the named Sonny he is completely different from the others. He was created to have a choice to follow the three laws. This was thought as something that could be dangerous for humanity. But it turns out that he was the best for humanity.
The other robots end up attacking the other humans; while Sonny was able to help the humans.
Basically he is the closest robot that could be related to a human. From able to relate to human emotions, to have dreams, to understanding that he is unique and can make a difference in the world. Just another reason why I see that if we get this far with our technology that we should give robot's the chance to be treated as human beings. Basically we are making them more human why shouldn't we treat them as one.