The fact that we have one terrible substance that is legal isn't a justification to legalize another.
except that alcohol currently and historically has generated huge tax revenue. if i were the alcohol lobby, i would make damn sure than no other drugs become legal and taxed.
(I believe Carvey originally made this statement about prostitution, but I'm not sure.)
For example, it frequently leads to a lack of believe in - or even just consideration for - how terrible substance consumption is, over all if not for the sake of nutrition.
http://cannabisandpsychosis.ca/more-information/what-do-we-k...
http://www.thelancet.com/journals/lancet/article/PIIS0140-67...
Hope this helps.