If that which is aware of fear is not fearful then isn't that which is aware of happiness not happy?

It seems clear to me that that which is aware of sadness, anger, or anxiety is not sad, angry, or anxious. But shouldn't this work the other way as well? Wouldn't this mean that that which is aware of happiness or joy is not happy or joyful? It feels like by this logic that mindfulness, when applied to positive states, nullifies them or diminishes them and that one wouldn't want to do this. If mindfulness diminishes the power of negative emotions wouldn't it diminish the power of positive ones as well? I'm not sure how this is desirable. What exactly am I missing?