Upload & Sell: Off
Well, who are you to decide whether the image is sufficiently valuable or worthy to merit a watermark? Should the creator of the work put it up to a popular vote before sharing it?
The question as you have posed it, assumes that people watermark their images because they think it has value and therefore must be protected from theft. But that's not necessarily a valid assumption.
Sometimes, people watermark their images as a form of branding. Some people feel it is about the principle. Some people do it because they've been burned in the past. And some people do it because they simply choose to and it's their right. It's not necessarily ego that drives the act. And even if it were, why should you care? If the picture has value in your eyes, then by your reasoning, a watermark is justified. If the picture does not have value in your eyes, then why would you care if a watermark is applied? It's already not worthy of your interest.