Is it permissible to abandon a brother who curses the religion and commits abominable acts?

Cursing the religion is a major sin that expels one from the fold of Islam. The default is that the perpetrator should be boycotted (الإهجار), but the benefit (المصلحة) should be considered in boycotting. Sometimes, boycotting may not yield its desired results and may instead increase the perpetrator's transgression, especially if they are among the common folk. Therefore, it is the benefit that determines whether or not to boycott, and the matter varies according to individuals and circumstances.