Most people who move on from one drug to the other usually started with marijuana use
The high that marijuana gives off no longer does anything for the user since he/she has built a tolerance to the drug
Drug history patterns usually exhibit trying a drug with less harmful effects then drug behavior gradually shifts to. using more and more harmful/addictive drugs
An increase in DUII's is very likely, however there isn't a system in place that tests someones current levels of intoxication like a Breathalyzer would do for alcohol
In general, marijuana stays in the system for weeks-months depending on frequency of usage, making it difficult to legalize without tools to PROVE if one is under the influence
Negative connotation associated with "supporting" drug use
Hard for police to enforce if they let their personal beliefs take over
The more people of age that can obtain the drug, the more likely it is for someone underage to get ahold of it.
Along with it being easier to obtain, legalizing marijuana will likely normalize marijuana use
People's stances on marijuana are an important part of their moral code
Much like the "pro life vs. pro choice" debate
Many people against marijuana are likely to do what they can to prevent its' legalization
second hand smoke
people didn't choose to engage in this behavior
Arguably more harmful than first hand smoke
Always feeling tired and "not all there" (if used chronically)
Depending on usage, can impact day to day activities and the desire to stay busy