Gaara and Sasuke situation are completely different, nor are they are comparable. Gaara did not kill people just because, Gaara when he was a child killed people because subconscious abilities of the Shukaku and that people fear the power of the tail beast. His own father told a big lie just to see if Gaara can gain control over the Shukaku, also later Gaara father hired assassins to eliminate him. Loosing his mother,his father lies, and not knowing of the truth of his uncle turn Gaara cold aloof person who kill anyone just prove his existence.
After first half of Naruto, Gaara work hard for 3 years to gain the title kazekage. Gaaras transition from a cold heart person to kazekage was well done. In my opinion Gaara had the best characterization in Naruto. Sasuke on the other hand was out of the blue(random) when Sasuke said he wants to become hokage. Because Sasuke in time skip flip flop a lot on what he wanted to do and his transition from bad guy to good guy SUCKED. Cause 1st hokage talked for like what 5 minutes, suddenly Sasuke change his mind(so much for Narutos job). Now Sasuke a good guy again whos wants to become hokage?! Are you kidding me?! Sasuke wants to become hokage, yet he does not care what his former teammates think of him? Sasuke does not DESERVE the title of hokage at all..