i don't smoke anything. never have. but i don't care what you do as long as you don't hurt someone else while doing it. you want to do meth? fine by me if you are locked in a room by yourself. so i really could careless if it is legalized.
but i do think the reason it is not legal has to do with taxing purposes. it is extremely easy to buy it one time (from a store so the gov't can tax you) and then just start growing it yourself. it isn't analogous to making your own alcohol. that is very difficult and can't be done in major batches without special tools. you can grow tons of weed in your basement or backyard. the second point to not being able to tax it is that if it was sold in stores and taxed it would cost more than just buying from a dealer. so how would the gov't profit from that?
i could possibly see it being legalized one day but it would still probably be illegal to grow it yourself (which would probably not stop many people) in an attempt for the gov't to make some cash.
i have also seen it's effects on people moving on to 'harder' drugs. i don't think it is too dangerous (no more so than alcohol) by itself but i do think it can lead to much more harmful substances and alcohol does not. i would say 50%+ of the people i know who started off just smoking pot went on to try other drugs. some wound up not being able to leave those other drugs so easily and it cost them big time.