If the comment had said "may or may not cause damage", that's a different thing. But the resulting phrase "probably causes permanent brain damage" is definitely a loaded statement to not back up with evidence.
It's not hard to find many journal articles that conclude it might -
DOI: 10.3233/JAD-160833 or https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6182105/
What journal articles conclude it might not?
That would change my opinion to "may or may not cause damage"
And the above journal also makes an effort to mention how "low to moderate quality" the data is.
For what is the world's most popular recreational drug, it's astonishing to see the lack of research committed.