As others have pointed out, Anakin killed murdered younglings, led to the death of Padme, worked with the Emperor to subjugate countless people for a generation and yet, he's redeemed within a matter of minutes?

I think this new trilogy is trying to show that things are more complicated than that. Luke, even after the events of RotJ, gives in to fear and nearly murders his nephew, cuts himself off from the Force, and resists training the one person who seems capable of slowing the First Order. And yet, he rises to the challenge, confronts Kylo, apologizes to Leia, and becomes one with the force.

I expect we'll see Rey embracing some of the dark elements of herself and Kylo finding virtue without fully abandoning or overcoming his demons.