Lots of good reasons IMHO. The author of the following opinion piece offers a compelling argument for making dope legal for adults.
http://www.cnn.com/2013/01/09/opinion/nathan-legal-marijuana/index.html?hpt=hp_c3
http://www.cnn.com/2013/01/09/opinion/nathan-legal-marijuana/index.html?hpt=hp_c3