The psychological term "splitting" occurs when you can only see somebody as "all good" or "all bad."It is a refusal to take in the complexity of the whole person: we are a mix of virtues and weaknesses.

Splitting is reduction, where the "good" people serve your ego (you protect them, but by affiliation, you define yourself.) The "bad" people are demonized, and any goodness they show is suspect, a front for evil machinations.