It's his blog. He can talk however he wants. You, however, don't have to read it.

When the blog post is under discussion, I think comments critical of it are just as fair game as ones which appreciate it. If the parent poster was emailing the author to make the same complaint then I think the "you don't have to read it" criticism applies, but not so much in a discussion forum. The point is to discuss what we think, even if that is a critical opinion.