Wikipedia:Category fight

A Category fight is a type of edit war which focuses on the placement of articles into categories. Often results when an editor wishes to claim the "prestige" of a particular category for a controversial subject, such as including a theory which is regarded as pseudo-science into a scientific category. Other times, the opposite is intended--an editor will attempt to demean a subject by grouping it into an infamous category--such as putting George W. Bush into Category:War criminals or such.

Sometimes, such actions are blatant POV and can be reverted on that basis; other times, such fights represent a legitimate controversy.