The selection bias in studies like these is massive. Including only people who actively planned to use psychedelics is a guaranteed way to bias your results toward people who are already true believers. People who voluntarily chose to seek out psychedelics, despite high legal consequences for doing so, are likely already convinced that the psychedelics will "work" for whatever goal they're trying to achieve. Selecting these people over the internet will only further concentrate the group toward people who enjoy discussing and researching this topic online. In short, they optimized the test group for maximum placebo effect.
It's fascinating to watch how internet comments will quickly tear apart any study of prescription medication that has obvious sampling bias, lacks control groups, and relies on self-reported information gathered from internet surveys except when the study tells people what they want to hear.
I'm all for the resurgence of proper, controlled research into psychedelics for treating mental health issues in conjunction with therapy. Let's get to the bottom of this and draw some scientific conclusions on the matter. However, questionable studies like this do more harm than good for the body of research. It may feel good to see studies that claim positive results, but the more we build the body of research on top of obviously flawed studies like this, the harder it is for serious researchers and lawmakers to take it seriously.