That's simply not true. Harvard did studies that showed long term pot used damaged the same area of the brain as is damaged in schitzophrenic/bipolar subjects.
Other studies have shown linkage as well.
5000 years of use
Are you just making crap up? Who's documented that pot was smoked 5000 years ago? And even if they did, what studies existed that they caused no harm?
Show me this study. I've gone through every existing research paper on this topic for the last 20 years and not a single one can show conclusive brain damage. There was one “brain scan” study but the technology was proven inaccurate.
The studies showing “linkage” show no greater link than can also be “proven” with tobacco.
Read the post I linked to. It shows schizophrenia rates have not increased even as cannabis use has increased exponentially around the world since 1970.
Evidence of Cannabis use has been found and dated to 2000-3000BC. There has never been a single person with bodily damage from cannabis. Research animals have been given constant doses exceeding anything a human can ever consume with no resulting damage.
Like those reliable studies on glowbull warming.....