Where do you think the "gravitational pull of the earth" ends? Hint: the moon is inside the gravitational pull of the earth... The danger is that things in orbit have velocity. A lot of velocity. Taking that nice F=mv^2 equation in mind you can imagine what would happen if a piece of space junk were to hit something we care about (or hit something we don't care about and create a lot more little pieces of junk that are now spreading out to cause more mayhem.) Space is big, and earth orbit is also a very big place, but there is still a lot of junk whizzing around up there and increasing the odds that something you forgot about will hit something you care about is counter-productive.