Why is marijuana illegal?

Why? What's the point of it being illegal? People still do it. And besides the people who are doing the drugs don't commit any real crimes the people who sell them do. I mean really its the gangs and stuff that sell weed and other drugs that are killing eachother all the people smoking weed r just sitting in there house getting high not doing anything bad. Its just completely ridiculous that marijuana is illegal. also as to my other point about gangs selling it if it was legal pharmacys tobacco stores everyone would be growing it and selling it not gangs. It could also be taxed and the governmeant would actually make money instead of reinforcing some bullshit nazi law.