What did I find out? You write sinners the same way you write saints.
Karl Iglesias did a series for Creative Screenwriting that broke character development into three elements and suggests that a writer must use a combination of these elements in order to craft ANY character that an audience will invest in.
Recognition - Understanding and Empathy
(1) We care about individuals we feel sorry for
(2) We care about individuals who display humanistic traits
(3) We care about individuals who have traits we all admire
Fascination - Interest and Intrigue
(1) We are interested in individuals who contradict themselves
(2) We are interested in individuals with internal conflicts
Mystery- Curiosity and Anticipation
(1) Plant unanswered questions about the past, present or future
(2) Create uncertainty about the past, present, or future
(3) Build anticipation about the future
Recognition, fascination, and mystery can invoke the same interest in villainous characters as laudable ones. The difference in not in the result but in the how you there. If we want to use recognition so our audience can identify with the character, we still need to get the audience to feel sorry for him, have him display some humanistic traits, or give him an admirable trait that the audience can hang their hat on. Throw in some fascination and mystery and you've got a compelling character. It's not harder, just different.
What I did notice, though, is that villainous primary protagonists fall into one of these categories. As usual, there may be more, but I've only identified these:
Hereditary bad guy - it runs in the family and he pretty much doesn't know any other wayI wondered if Bourne Identify and The Long Kiss Goodnight might qualify as some kind of amnesiac bad guy, but they were bad in a former life, so they aren't villainous characters. Or, are they?
Justifiable bad guy - he has a good reason for being bad like vindication or rescue
Misunderstood bad guy - he's not really bad, he just looks that way
Involuntary bad guy - he was forced into it, had no choice but to participate
Accidental bad guy - he didn't mean to enter into the lifestyle but is now trapped
Understandable bad guy - he had a choice but the viewer can easily understand why he took the less noble route
Lesser bad guy - our protag is the least bad of a whole community of bad guys
Loveable bad guy - yeah, he's unscrupulous and chooses to be that way but we don't really care
My favorite all time evil protagonist film -- Whatever Happened to Baby Jane? I'd say she's "involuntary" since she's mentally ill.
What have I missed? In your favorite film where the primary protagonist is villainous or dastardly, does he or she fit into one these categories or does the list need work?