its a difficult question, with a clear answer if you think logically about it, and take into account UK law. It should be legalised for general used, with restrictions placed on it including age, and how much you can buy at once.
No-body can justify having both alcohol and tobacco legalised, but not cannabis - in any state, doesnt matter if its just some crappy indica depressing green, a high grade skunk varient such as AK47/white rhino(best ive tried that btw, much better than super skunk ) or any of the types of hashish.
I openly smoke it when i get the chance ( a few hours off), and I don't see it as a problem. I'm not addicted (can go for indescriminate periods of time without cravings etc) and have a great time using it. Its especially good at stress relief, feel so much better sparking after a particualrly bad days work. Just like some people reach for the bottle, a fag, food, etc, i come home to weed
My use is moderate - 1/8th of an oz every 1-2 weeks. Ok so thats gone up since i first started but its been sitting there for a while, and i dont think its going to change much.
As with any drug, i think the problems lie more with overuse than anything else. Alcohol is fine for a few drinks a week - the problems appear wehen you overindulge (ie get drunk). Ciggs are different in that each one causes you a fair bit of damage, but heavy use will still do you a lot more damage than light use.
Most of the medical problems with cannabis are because the majority of people smoke it through joints - mixtures of cannabis and a small amount of tobacco. People often put in more baccy than needed (forgetting why its there in the first place, to help keep the joint burning longer) causing health risks that wouldnt be there if it was smoked using a pipe or bong. Granted my preference is to use it through joints, but ive used bongs/pipes too.
What about the social problems..again this is related to heavy use. Yes if you smoke it 24/7 its going to mess you up. I know ppl who this has happened to and its not nice; one of them spends £180 a week on it - thats 2oz a week! just a bit of overuse there methinks..
As for it being a gateway drug? thats bull tbh. The only reason why this might happen is because the dealers who sell cannabis normally sell other stuff too. They might offer you some and bang there you go. 99% of users have enough common sense to stay away from it though..and those that don't would probably have gone onto harder stuff anyway.
light to moderate use doesnt cause the problems mentioned in your essay - theres no CONCLUSIVE proof for any of the arguements against it, its just a shame that i doubt the government will ever see that.
legalising it could provide us with a stable, guarenteed supply - i'm thinking like holland here where you can walk into a coffee shop and just openly ask for 1/8th of White rhino or whatever, whereas here its a case of buying what you can get - which is often crappy mids that could be anything (unless you know a grower or big dealer). Plus they could tax the hell out of it which has got to be a good enough reason for any government