Welcome to the server.
I am going to agree with zircon, and add that saying it's not a "spawn door" borders on semantics. In my opinion it is completely analogous to the shortcut doors on Dustbowl 3 and Goldrush 3. They're shortcuts, and they close after a certain point is capped, they can be circumvented by taking a much longer route, but that does not justify sticky-camping them. The problem is especially exacerbated on Badwater by the fact that it's so open that a demo can very easily jump over enemy lines to get to it, and the door is far enough behind the front lines that you'd have to waste a sentry for the sole purpose of protecting it.