A blog is not a discussion forum or a message board. Blogs can be used for those purposes just as a knife can be used as a screwdriver but it is better to use the correct tool.
Comments on a blog may be unmoderated, or moderated in various ways. Most people do not allow abusive or spam comments. On a blog with comment moderation, these will be rejected before they are posted. On a blog without moderation, they will be deleted as soon as they are found.
Some blogs have lively discussions in the comment boxes. When there get to be a lot of comments, the author has to decide whether they have time to moderate them all. The author will also take a view on whether the comments add enough value to the blog to make it worthwhile doing the extra work of checking them all.
There are other reasons why a blogger might reject comments. If someone posts a purely negative comment on a post, the author might choose not to publish it (people who post such comments are sometimes referred to as “trolls”). The author has taken time to write the posts; the blog has built up any readership it has through the quality and popularity of the author’s writing. The author is under no obligation to give someone else the benefit of this readership simply to launch an attack. After all, the author of the comment can set up their own blog. If their views or posts are popular, they will build up their own readership.
Having said that, there is of course the question of genuine discussion. A blogger might or might not want to allow that – it is entirely their choice. Often, blogs suggest a word limit of 150 words or so for comments. Many authors close the comment box after a certain period of time to save having to check old posts for new comments.
An author is bound by the usual moral requirements that apply to human discourse generally. But beyond that, an author is free to write on whatever they choose. If people want to read it, they can. Sometimes people forget this. A famous interaction on Open Book, Amy Wellborn’s influential and hugely popular blog, is a good illustration. A comment from someone called Francisco included the discourteous questions:
Why do you feel it important to point out to us that this leaves you feeling dry? Do you want our approval?To which Amy replied,
Francisco- I'm a writer. I write. This is a blog. I write stuff on it. People discuss it. It is not a big deal.So much for comments in general. This post should be read in conjunction with the next one: Comments on this blog.