Sure, there's no guy with a gun forcing you to read it.

But we're on a site about sharing content for intellectual discussion, right? So when people keep posting the same garbage without labeling it, and you figure it halfway though the article, it's frustrating to find out you wasted your time.

To use your soup analogy: imagine this was a website to share restaurants. You see a cool new Korean place upvoted, so you stop by there for lunch sometime. You sit down, you order, and then ten minutes later, Al comes out with his trademark thin, watery soup again.

In that scenario, it's entirely reasonable to leave a comment, "Ugh, don't bother with this place, it's just Al and his shitty soup again."