Why would a DALEK want to exterminate it's mirror image?
The only purpose of a DALEK is to rid the cosmos of everything NOT DALEK so that it can become the supreme master of the universe.

What I don't understand is why some people have such a problem with patents. Can anyone please explain this to me?
Well, to be a little RMS with you, it's not only about making money, and thats about everything it comes down to. You see, there are people out there who wish that software is free so that consumers and developers can share and develop it further and faster than with a closed propriotary software solution. It's the same method used for development of science.