Puggo - Jar Jar's Yoda said:
Good people turning to evil is an age-old theme that has been done successfully in thousands of movies. There were so many ways it could have been done. George managed to find just about the only way to screw it up.
Can you name some, Puggo? This is not to challenge what you said, but I have stuggled to put a good list together. The last time I tried (3 years ago: http://originaltrilogy.com/forum/topic.cfm/Fall-to-the-Dark-Side/topic/8843/ ) I decided that storytellers often tell convincing stories of redemption, and that people are apt to believe them... but it's really hard to tell stories of "the fall" without some kind of trick. They were poisoned, a dark presence made them evil, they weren't in full control of their mind or actions, etc...
If you can list some well told "good person turns to evil" stories, I'd love to hear them. King David is one of the only ones I can really think of.