Ever since we saw Jacob and his buddy chatting on the beach dressed in respective white and black, many people have jumped straight into saying that those characters represent pure good vs. pure evil.
But, I dunno, I'm not ready to say Jacob is some kind of 'supremely good' character. We've seen him do stuff that I would regard as a bit shifty.
He distracted Sayid so that his wife would get run over and killed. He encouraged Sawyer to finish his letter so he could spend all of his youth stewing in vengeance and ruin his life by becoming a con-man. He pretty much rewarded Kate's dishonesty when she stole that lunchbox as a kid. And he was kind of a jerk to Ben after he poured his heart and soul out to him under the statue. ..."What about you?"... pfft. What about YOUR manners, Jacob! Besides, he is supposedly the leader of 'the Others', who have proven themselves to be a bunch of lying, manipulative, baby-snatchers! Ok I'm getting quite flippant now, but my point remains.
In the same way, I'm not ready to say the MIB/UnLocke is a big, evil 'force of darkness', just because he plots to kill Jacob. We can at least say he's not very nice. That doesn't mean he's the spawn of Satan. Who knows, he might even have an understandable reason for wanting to do such as thing. I mean, how many characters on Lost have wanted to kill someone over the course of the series? Pretty much all the main characters. We wouldn't refer to them as pure evil- they’ve just got 'issues'. I think Lost is more complicated than goodies vs. baddies. All the characters are complex, and just like real people, some parts of them are good, some rotten.
The 'black and white' motif has been used throughout Lost, not necessarily as good vs. evil, but certainly of rivalries and counterparts. Think of the relationship between Ben and Widmore. Neither is the 'good guy' or 'bad guy' (they're both quite terrible actually), but they have a personal rivalry with many factors at play. I like to think of Jacob and MIB in the same way. It may be more complex than we think.
Just my thoughts for the evening.