Why am I not allowed to be angry?

It's possible that your friends may feel uncomfortable or defensive when you express anger toward something they did or condoned because they may perceive it as a criticism of their actions or values. People have different ways of responding to and coping with anger, and some individuals may find it challenging to handle direct confrontation or criticism, even if it's expressed constructively.
some people may have difficulty accepting responsibility for their actions or may feel guilty when confronted with the consequences of their behaviour. As a result, they may react defensively or attempt to justify their actions, which can lead to tension or conflict in the relationship.
It's important to communicate openly and respectfully with your friends about your feelings and concerns. Expressing anger in a constructive and non-confrontational manner can help facilitate productive conversations and promote understanding. Listening actively to your friends' perspectives and being willing to engage in dialogue can help foster mutual respect and strengthen your relationships over time.
If your friends continue to react negatively or speak ill of you when you express your feelings, it may be worth evaluating the dynamics of the friendship and considering whether it's a healthy and supportive relationship for you. Surrounding yourself with friends who respect and validate your emotions is essential for your well-being and happiness.