All four of those bullet points are flawed, and I think that's the point. They are _perceived_ reasons to not blog, rather than actual, legitimate reasons. That's my take anyway.
Instead it seems to assume they are truths but argue that you shouldn't care that your thoughts are unoriginal and others laugh at your stupidity.
And even if you know they're flawed, it can still get in your head and discourage you, so the author provides a different list of reasons to still blog in spite of that. It's not meant as proving/disproving any of the points, but simply as motivation to keep going.