Personally I think it's valid to consider selection-bias effects in authorship -- in general, things are written by the people who are the most excited about the topic, which leads to there being a bias towards excitement. I don't think it invalidates the research but it feels like a valid point.

I think an interesting observation is that this anti-psychedelics post is written by someone who doesn't even want to try them, so this argument of his also says to treat this blog post with skepticism.