It's also why I found the TV series _Angel_ (the _Buffy_ spin-off) so unsatisfying. There is a truly fascinating story to be told about a vampire whose soul has been restored to him, and who is always at war with his own evil nature. But _Angel_ is not it. Instead, the eponymous character is essentially entirely good except when some supernatural agency transforms him back into Angelus, his evil form. All the conflict is externalised.
That's a particularly surprising and disappointing mis-step given _Angel_'s provenance. Joss Whedon is exactly the kind of person who I'd have expected to be interested in exploring the _inherent_ contradictions within the Angel character, and showing how they are analogous to the questions that we all face.