A: Nothing really. A Newsgroup, like life itself, is full of morons. Just ignore them. Don't respond to them. Even better, don't waste time reading their comments. They aren't likely to be able to contribute anything worth your time.
Q: What can I do about this?
A: Some newsgroups by their nature attract people who are not accustomed to following a logical progression of written comments. They either lack the intelligence to do so or are just too lazy. They read and reply to only the last comment without any concern for, or attempt at, understanding previous comments. Often their contribution is useless.
Q: Then why are there some newsgroups with a lot of top posters?
A: Because it destroys the logical flow of a thread of comments.
Q: Why do so many people object to top posting?
A: Writing your reply to a message above what you are referring to rather than below it.
Q: What is "top posting"?