Cultural relativism is an anthropological issue which aims to explain the equal validity of all cultures stating that beliefs, customs, and morality in every culture are relative and that a given way of life is as valid as any other. The theory has long been criticized for its inability to resolve the conflict between cultural relativism and universal rightsand has been berated for two different but complementary reasons both at theoretical and practical levels.
At the theoretical level, cultural relativism ignores reason and objective reality. In point of fact, the theory assumes that objective reality is an independent entity separate from man's mind, feelings, desires, etc.Accordingly, every individual perceives reality based on his/her own cultural views . Notably, such a position makes the perception of reality subjective and culture bound, which is uniquely interpreted by the perceiver. Differently stated, realities and experiences are culturally defined and culturally conditioned.
At the practical level, cultural relativism approves of the most barbaric acts of violence and aggression. This stance makes the the oppressed totally defenseless against the oppressors because cultural relativism does not question the moral elements underlying aggressive , inhumane acts of violence and aggression.
On this basis, as you have rightly observed, cultural relativism has a contradictory nature which shakes the most fundamental aspects of universal rights. No wonder, it is generally agreed today that cultural relativism is a theoretical relic symbolizing one of the most destructive mistakes of human theorizing and philosophizing. If you don't believe this, just look at the gruesome wars destroying innocent lives all around the world today.
Tolerance is the core for every human (not religion ) we came together as a civilization (religion later) . If there is lack in understanding that then , it leads to suffering .