I agree this can happen. I don't see why it's important. If someone else won't take you seriously just because you're not a certain rank, their opinion of you probably isn't worth your time. (With obvious exceptions, such as if you're trying to make criticism about a black belt form and you're only a red belt).
It's been pointed out above the benefits of rank in a large school, with a curriculum designed around each belt. Rank is important because it's how you learn new concepts and advance your knowledge. But it's also important politically within your art. In the KKW, I'll have more rights as far as teaching goes the higher the degree I am. This is why I have my eyes set on earning 5th Dan and the rank and title of Master. It's not because of my ego (ok, there's a little bit in there). It's because I'll have the option to run my own school at that point.
I mean, I could always open my own school under my own art, but I think it carries a bigger weight if I've got that Master certification.