One thing that bothers me with studies on MDMA harm is that they tend to look only at regular/frequent users, rather than occasional users. For example, the study this post cites for MDMA causing decreased attention and general intelligence only looked at subjects who used it at a minimum twice a month for 6 months or more than 25 times over two years [1]. It's still unclear whether single or infrequent (like once every 2-3 months, which is common advice for recreational MDMA usage) use is harmful, which is important to determine for progressing MDMA-assisted therapy.
I don't understand how the author can come to this conclusion after describing almost every mentioned paper as unreliable for one reason or another.
As far as I know there is still very little in the way of consistent and/or rigorous evidence that even moderate recreational doses are harmful.
I would argue that if it is this uncertain as to whether or not the drug is harmful, then it is unlikely to have significant detrimental effects. Subcultures tend to build stigma toward obviously dangerous substances - most drug users would caution you to stay away from heroin or meth, for example, because the damage is obvious. If harmful MDMA effects are so subtle as to be effectively undetectable in the collective anecdote of millions of recreational users, then at the very least occasional use must not be so risky.
[1]: https://www.ncbi.nlm.nih.gov/pubmed/10811694