Leaving a situation doesn’t require a farewell speech. Walking out calmly is a whole statement.

Exits do not need justification to be valid. The urge to explain yourself on the way out usually comes from wanting agreement, and looking for agreement keeps you in the room longer than you meant to stay. Leaving quietly says the same thing with less to argue about.

If you have decided to go, go, and let the decision carry itself. A short sentence about needing to head off is enough, and you owe nobody the reasoning. The people who want a speech were not going to accept one anyway.