since I dont read the manga, I'm not too familiar with any of the stuff beyond this ep.

Itachi kills people to test his ability. Kind of an odd approach, but it fits for a character like Itachi. It sure as hell is better than having a bunch of evil people that just want to destroy the universe. Those people blab on forever and just wont shut up, and therefore are hated.

But because Itachi is somewhat mysterious and very dark, it makes him an interesting evil character, as opposed to say, the likes of a Cell or Frieza.