Marijuana is not a gateway drug. Opioids are far more dangerous. You want to know the truth of drugs? Watch the art created by them. Watch or read books and movies created by the users of the following drugs: a ”stoner”, an alcoholic, a heroin user, cocaine, and meth. It is an excellent way to understand the use and impact of these drugs.
That doesn't include why marijuana was initially made illegal. It had nothing to do with its impact on behavior.