To what extent is it sound to train oneself to love every Muslim monotheist, while remembering that everyone falls into sins? And if it is permissible to hate a Muslim for the sake of Allah, is it permissible to display this hatred? And is a person rewarded or condemned for their love or hatred of their sinful Muslim brother?

A Muslim is loved for their Islam and faith, and is disliked to the extent of their sins and disobedience. There is no necessary connection between internal dislike and its outward manifestation. The outward manifestation, through abandonment and turning away, depends on what serves the greater good. Thus, it is shown to deter the person being abandoned from sins, if that indeed deters them; otherwise, it is not.