No one's saying that simple comments aren't allowed, but I'm not sure that your simple comment contributes much to the conversation. Maybe if you explained why you thought that you think that Facebook is beginning to worry about serious competition, you wouldn't get a reply asking what you meant by your otherwise simple comment.

When someone nitpicks at a tiny element of a larger post, that's pedantic. When all you posted was something tiny, however, you're inviting further inquiry by being unspecific and vague.

The low karma he would supposedly get from simple comments should be feedback enough.

pg, the site founder, observed once that longer rather than shorter comments tend to be valued by other participants here (as judged by comment karma scores). The subset of HN participants who read my comments appear to share this opinion, as my longer comments do tend to gain more karma than my shorter comments.

To explain to you the specific reaction to your one-sentance comment (great-grandparent here, immediately below the submitted article link), I really couldn't tell for sure if you were being ironic or meant the literal meaning of the sentence you posted. A longer comment usually makes that of issue more clear, which is important in a medium where we are not speaking face-to-face and seeing each other's body language or hearing tone of voice.