Yeah, I would guess people don't like "Hey, I didn't actually read this, but here is something that I imagine must be related." (Even if it does turn out to be relevant and worthwhile.)
True, but I can also see it from the other side: "I feel that I have something worthwhile to contribute, but I don't have time to read the entire article, so I'll just post it here in the hopes that someone finds it interesting/relevant."
I think that it would be somewhat of a stifling approach to just make a blanket proclamation that no one can enter the discussion unless they have full read the article.