First and foremost, marijuana is already associated with more abuse and dependency (now called substance abuse disorder) than all other illegal drugs combined. Roughly four out of seven problem users [3]of illegal drugs are using marijuana. This is a dangerous blind spot exploited by many legalization advocates (although some [4] of them are now warning about the growing risk of heavy marijuana use under legalization)....
Links
[1] http://www.foxnews.com/opinion/2018/07/03/ex-drug-czars-bill-bennett-john-walters-mr-trump-please-don-t-legalize-marijuana-at-federal-level.html
[2] http://rethinkpot.org/tags/bennett
[3] https://www.samhsa.gov/data/sites/default/files/2016_ffr_1_slideshow_v5.pdf
[4] http://www.slate.com/articles/business/moneybox/2016/11/america_is_legalizing_marijuana_wrong.html