It seems to me that forgiveness is a good thing when someone has been really unfair to me. Yet, anger is a natural part of reacting to injustice. So, to forgive, does a person have to suppress anger? If so, then forgiveness seems like it is psychologically unhealthy.
When people forgive, the goal is to reduce or even eliminate the anger, not to suppress it. When we enter a forgiveness process, we look first at the anger, which is a way of acknowledging that anger, not suppressing it. Thus, when we forgive we do not suppress anger. Forgiveness, then, is not unhealthy in that it suppresses anger.
For additional information, see The Four Phases of Forgiveness.