Actually it's pretty conclusively proven fact in terms of long-term, chronic (no pun intended) users, with statistically significant data. Also proven to decreases language skills and has a memory impact. Again, this isn't casual once a month users, but frequent users.
Conclusively proven fact. Lol
Show me unbiased data; not a Pfizer sponsored study.
Does it affect some negatively in those ways? Absolutely. Same with alcohol. All depends on the individual. You can't have "conclusive proven facts" when the results vary by individual. Science doesn't work that way.