Use of marijuana is, in my opinion, stupid. It impairs your mind and can prevent people from doing truly fun things. But it's no worse than cigarettes or alcohol. In fact, it's better. Cigarettes are more dangerous and alcohol (which is very, very prevalent in high school students where I live) is deadly.
At my school, there are MANY people who use marijuana. I don't (because I think it's stupid) but a lot of effort and money is spent by the city and police (who have plenty of other much more pressing matters) to bust people using and selling this drug. It should be legal and government regulated (the way it is in the Netherlands). Making it legal might also decrease the use of it by rebellious people.
If someone wants to start using marijuana, he or she should know the risks and know why they're using it, making informed decisions. It can still be dangerous if one drives under the influence of it, among other things.
On the other hand, if it were legalized, I doubt underage people could legally use it, and they're the ones who like to rebelliously use drugs like this. Marijuana kills brain cells and causes laziness, and some drug users just want more.
So although I guess it should be legalized, I strongly discourage its usage, and believe it should be discouraged by communities. In my opinion, drugs are used as a substitute for the real, fun things in life. So instead of using drugs, why not find something fun to do rather than spend your time in a drug-induced reverie?