I'm not entirely sure whether im on the side of legalise here, but maybe more leaning towards decriminalisation, or possibly the same kind of laws as Amsterdam, where it is served in some cafes, and you are only allowed to do it in these cafes or in privacy, not on the streets IIRC. IMO this wouldnt really do much harm to anyone apart from the person smoking it, because they are smoking it. This kind of brings me to my next point:
Sure, smoking it is dangerous to your health, since no smoke is good for you, or at least non-harmful, but there are actually some surprisingly good alternatives to smoking it, the best being either baking it, or using a vaporizer, which cuts the smoke out totally, so you are just getting the cannabinoids(sp?) or THC (not sure which) from the marijuana and not all the tar and crap as well. Therefore i think it should really be individual choice if the marijuana is smoked or whatever if it ever was decriminalised, just the same as it is with cigarettes.
As for addiction, i used to smoke it quite heavily i admit, I have stopped now and i can honestly say that i never felt any withdrawal symptoms from it, never felt like i actually need it at any point, and as has been found somehow through research, it is only a psychological addiction, which would probably be hard to quit for people with a slight or mental problems anyway.
/rant over now, i just thought i would let you know my point of view on the subject and how i feel.