If you're going to write a blog post, why not write a blog post? They offer free hosting at a variety of places. The only possible reason that I can think of is that more people might read their comment here. So that's spam. Great. We know what to do with that.
Comments offer you an opportunity to communicate with the author, or provide an alternate point of view to something he or she said. If you talk over that person's head, and rebut someone who's not even present, well -- that's just plain disrespectful.
One person said in all seriousness (apparently) that someone else's opinion was invalid because they were probably autistic. Can you imagine, a medical diagnosis in a comment? Oy. Even if the person is qualified, how is that appropriate?