I agree completely. Bitterness is cancerous. It festers and infects our daily lives. Anger on the other hand is a more natural emotion. No one can stop themselves from feeling anger, but precisely as you say it depends what you do with that anger. If you lash out in anger and bitterness you do no good. However if you use your anger to fuel you to do something to improve the situation than you are using your anger wisely. For example sprinting in a race and losing. Your angry that you lost so you train harder so next time you can do better. If you were bitter you might just instead attack the victor and do harm instead.