It's not that he shouldn't express his views in a blog. The part that feels shifty here is that he's not disclosing his position in the space in his articles. I think most people are at least somewhat susceptible to "It is difficult to get a man to understand something, when his salary depends on his not understanding it." so a disclosure of interest is useful to frame thoughts on a topic.

I didn't know about any of this until @capableweb brought it up. It explains a lot more about this series of blog posts.