Saying that LOST is just about good and evil is like saying House is just about a bunch of attractive doctors.
Think about the ways they have demonstrated to us in the past 6 seasons how the struggle between good and evil is something that rages inside each of us every day. Think of the ways that LOST has made us think about tough decisions, and what horrible things we will do for our loved ones (Walt/Michael). Think about the themes of free will - the trait that makes humans unique, and the trait that allows humans to be evil or good (Ben letting his daughter die, Kate kills her abusive step-father, Charlie dies to save the rest of the survivors, etc). Is it evil for a human to make a terrible mistake if they try to redeem themselves? Wouldn't you kill for a chance to live your life over again, knowing your mistakes and misdeeds? Wouldn't you do anything to see your loved one again? Does that make you evil? These are the themes that LOST is presenting to you - it just boils down at the highest level to good vs. evil - but doesn't everything?
To say that LOST is just about good vs. evil is a dramatic understatement, and it means you missed the whole point of the show. LOST isn't about good vs. evil at that basic a level - it's about good vs. evil at a personal level, and how our decisions and actions tip your personal scale in one way or another.