Many people have built their opinion on marijuana from the propaganda that has been propagated over the past several decades. However, much of this propaganda is refuted by case studies now that marijuana is being more widely used.
Take Massachusetts for example - a number of towns have placed moratoriums on letting marijuana-related businesses operate in their municipalities partly because they believe kids are going to be getting high. They have a fear of marijuana engendered by years of prohibition and propaganda. However, people are just going to go purchases their marijuana products in towns where its legal. In a few years, these towns placing moratoriums on weed-related businesses are going to look back and say "damn, we missed out on a lot of money". Because the negative externalities being communicated by those taking an anti-marijuana stance are just not real...