The trashing of space is a "Tragedy of the Commons", a common theme throughout history. It happens because of those who are selfish and do not care for the overall good of humanity.
The only cost effective method of removing space junk is to hit each piece on its leading face with a short, very high intensity, blast of laser light which will alter its orbit sufficiently to bring it down. This could be done from the ground with adaptive optics or from space.
The energy costs of matching the orbit of each piece, grabbing it and returning it to Earth is currently prohibitive.