There is a MEL that lists what is required for a flight. The inop lav may be okay up to a certain length of flight, but then it's up to the Captain whether to take it. Most folks want to make their connections so they vote to take the inop lav I bet.

Now, if you didn't want to fly with that, I think the GA was a little harsh in not letting you go on a different flight. I think all of JAX is UX, so that doesn't surprise me

I would write United and tell them the story.