Every human contains good deep down inside them, as well as a uniqueness in perspective and views. So much of a person is hidden below the surface with layers upon layers concealing them. Each individual has potential to undertake so much, both good and bad, yet at the same time everyone has many inevitable weaknesses. Two things that really define a person is their love and hate...with love they can produce so much good, so long as their hate does not consume them and drive them to cause destruction. In reference to the title, Darth Vader was neither 100% good, nor bad. He started with good intentions but hate drove him down a bad path. Nevertheless, in the end of Star Wars the character showed that there was always some good left inside him and he returned from the Dark Side. This demonstrates that humans (as well as Darth Vader) are not necessarily good, nor bad, and much of their standing depends on what exists beneath layers and layers: in their core.
