almost everytime gaara was about to kill, he claimed he wanted the blood, sometimes his face looked weird at times, kankuro and temari was worried of the monster coming out, those weren't human looks he was making, it had a LOT to do with the monster inside him. that's the only reason he appeared so scary to everyone, if he was hated the same but had no monster inside him, it would look different, even his blood thirst would most likely have been removed. he also wouldn't have had to worry about never getting sleep a day in his life, lol.
sasuke knows full well what he's doing, he has no monster to blame, he is his own monster, what makes him even more evil IS that he was once good, he was BEST friends with sakura and then threw it away in a heartbeat, he no longer cared for her life. and that's what makes him more evil, gaara never experienced love, but sasuke did and threw it away for hate, he lives on it now, it's the only thing that's really making him stronger. in the fight with danzo, sasuke was goner, but his hate made him more powerful, that isn't the case with gaara. sasuke actually relies on this stuff like it's a drug to boost his strength.
