It should totally be legal. The only logical explanation why it is still illegal is because of pharmaceutical companies and other companies like paper etc. which could go out of bussiness because of it. Seriously, in our day and age there's so much scientific proof for marijuana having more pros then cons that there is absolutely no reason for it to still be illegal, it's ridiculous.
Though I'd actually be up for all drugs being legal or at least decriminalized. Listen, it's your life and it should be your choice, and with all the information you can get on drugs (talking about the "hard" stuff) you're still dumb enough to do them... and even if they are illegal, if you want to do them, you will do them, if you don't, then you wont do them legal or illegal. And you shouldn't be punished for it by going to prison (unless ofcourse you hurt others), instead you should get help by going to rehab etc.