Why? Oaths don't stop people from doing whatever they want. At most, it just prompts them to provide some rationalization for why whatever they went to do is right, and was really someone else that broke/invalidated the oath first. Thus their character was perfectly morally justified in doing what they did anyway.
Why not? Such justification is good. Plus you can call them "Oathbreaker" forever and with Baal the Betrayer and Jonsu the Usurper we need a good epithet for Enoch.
