Arguing about whether marijuana is safer than some other drug is a ridiculous argument to have. What’s important is whether smoking pot is harmful and there’s some evidence for that.
https://www.ncbi.nlm.nih.gov/pubmed/26884547
https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6428a6.htm?s_cid=mm6428a6_x
http://www.lung.org/stop-smoking/smoking-facts/marijuana-and-lung-health.html