In We, Zamyatin shows, through D-503’s transformation from an almost emotionless individual to a compassionate and loving one, that the One State’s utilitarian ethics conflict with the values of compassion and love.
An essential characteristic One State is that it aims to provide collective happiness. The One State operates by a utilitarian ethic under which the proper course of action is the one that produces the most happiness for the largest amount of people. You can find evidence for this interpretation page thirteen when D-503 expresses vexation with ancient laws: “To kill a man, that is, to decrease the sum of human life by fifty years—this was criminal. But decreasing the sum of many humans’ lives by fifty million years—this was not criminal. Isn’t that funny?”
D-503’s surprise at these ancient laws reveals what he things the proper laws of the One State are. He implies that killing a single man is less reprehensible than doing a lesser harm to many more people. This sort of estimation is typical of utilitarianism because it can be reached by a calculation to determine which action has a greater effect on gross happiness.
The values of love and compassion are not guided by these calculations and they’re typically focused on individuals, not collectives. As the novel progresses, D-503 devotes more of his records to individuals (R-13, I-330, 0-90) rather than to the whole of the One State. He also begins to express compassion and love for certain characters, I-330 in particular. He falls uncontrollably in love with I-330 (he mentions it on page 57) and the deeper he falls, the less he is able to be a functioning member of the One-State, he has to be listed as sick, he cant go to work, cant sleep when supposed to etc.
This simultaneous transition from emotionless to loving and function member of the State to delinquent is how Zamyatin’s intended to show love and compassion are incompatible with the One State’s utilitarianism. As D-503 develops these emotions, he himself becomes incompatible with the One State.