There are a lot of people that use marijuana illegally right now. But there are also a lot of people who may be interested in marijuana but do the right thing and stay away because it is illegal. If you take away the illegal part many more people will be open to trying it.
I have never used marijuana due to a fear of failing a random drug test or being caught with it and it ruining my future. If it was legalized, I would probably at least try it to see what it was like. I don't think it would significantly increase use though.
I think decriminalization of marijuana is a good idea. There are too many government resources being used to prosecute marijuana users. At the same time, i believe that decriminalization of marijuana would encourage many new people to try it. The negative stigma associated with marijuana because it is illegal would disappear if it were to ever be legalized.
The reason this is such a talking point is because there are so many people smoking it with the laws the way they are now. There aren't many people that really want to smoke pot but don't because of the penalties behind it, you either want it or you don't. This would just do what it says and reduce penalties, not increase usage.
Decriminalization of marijuana would not increase drug use. The people that want to do the drug already do and have their own connections and ways to get it. I think legalizing the drug would just make it less dangerous to possess. However, legalizing the drug would not lead to an increase in its use.
Decriminalization of marijuana possession would come with heavy regulations and plenty of taxes. It would also make the use of marijuana less attractive to those who just want to rebel or live dangerously. This would cut down on many people who couldn't afford to use the drug and those for whom the drug would no longer be attractive.
Many of the remaining people are already using marijuana and would just be doing so publicly and paying a lot of money for the privilege.
At a certain point, law makers have to understand that, barring truly damaging acts, laws are going to be far better and more successful being descriptive rather than proscriptive. Marijuana is not murder, or terrorism - no law needs to be in place that explicitly prohibits it, and an allowance of it would simply be recognizing what is already happening in the country.