Originally Posted by
TravelerMSY
It sucks. Agents have wide latitude in interpreting the rules. Their goal is more to avoid government fines if you’re denied entry after they transport you, and some cultures are more rule-based than others.
I disagree on this particular issue. The OP admits their passport was, in fact, damaged. The airline is responsible for verifying documents before an international trip. Since assessing damage is difficult and Delta can be subject to a heavy fine if documents are not in order, I don't blame the agent for being overly cautious.
The OP can certainly complain, but the agent and the manager will say that the passport was damaged and that will be the end of the investigation.