Some roleplayers like adhering to good/evil archetypes, while others like to explore more nuanced morals. Some begin their gaming careers at the nuanced end, but many develop from the former in their initial forays into gaming, towards the latter as they become more experienced.
It's all good, as long as people are having fun!
Han: I don't remember all that.
Darth Vader: I'm just filling in the details we didn't want the others to accidentally overhear from the kitchen.
Luke: So you and Jim cooked this up?
GM: I was there too...
Darth Vader: Of course.
R2-D2: Okay, but why did you switch characters?
Darth Vader: We wanted Vader's identity to be a complete surprise.
Darth Vader: I hate it when a lead female gets killed off just when she's getting interesting, and Anakin's story was done, so...
Han: And I wanted to play a good guy.
C-3PO: Han is a good guy?
Han: Kyle Katarn was. And Bria Tharen. And Bail Organa. And Captain Antilles.
Han: Then I got sick of playing goody-goody chumps and dying, so...
Chewbacca: There is a middle ground, you know.