I had similar experiences with every group project, where one or two people have to do all the work. I asked a teacher about it once, and his explanation is that it's a lesson for working in the real world. Really drives home the saying "those who can't do, teach". I think it would have been more moral to do what your teacher did and actually validate contribution, instead of intentionally teaching students that you can screw around at someone else's expense and get away with it.