There may be an "is -> isn't" or "can -> can't" issue in the line I quoted, but I don't think so -- the rest of the sentiment in that article seems to be a specific case where the poster believes that someone is making an error of offering an opinion without experience (which I agree is an error), which makes sense (though, I'd obviously argue, represents an overgeneralization from a valid example) if its supporting a generalization that opinions without experience are invalid, but, without some "but" or "on the other hand", etc., doesn't make a lot of sense if the thesis it goes with is that some such opinions are valid.

So I don't think I misunderstood it.