Note that Citra's main reasoning for wanting to be a scythe is to live a life of purpose. After her training, she understands even more deeply that the rest of humanity is just existing and has little purpose. Within the logic of their world, scythes are the only people who have a purpose, even if what they do is morally repugnant to most people, including some of the scythes themselves. Despite this, Citra's realization that she has a crush on Rowan shows her that she's still a normal, if righteous, teen, and that she'll have to fight those impulses to become a scythe.