Not to play devils advocate or whatever... also as I write I realise this is gonna get a bit wall-of-texty.
On the subject of soft drugs, etc... I know it's a bit of a de facto response but if you spent a large portion of your day drunk over a long period of times there would definitely be some adverse effects, as there would be with if you were high. The problem most people have, I find with the 'it can lead to health problems' argument is that so does everything. Run too much and it'll fuck your knees up eventually, drink too much and you get liver cancer, and so on. People can choose to drink excessively and legally knowing these health problems are going to beset them, and the government can let them and pay for their healthcare (in the UK) - why can't people who want to take cannabis do the same? Also I will admit that cannabis does provide a gateway to harderillegal drugs, without a shadow of a doubt. However, tobacco and alcohol are providing a gateway to cannabis. How many people who have never smoked nor drank before would wish to indulge themselves with the vices of life start with cannabis? True, once you take cannabis, find someone willing to provide who's not a pain in the ass, find somewhere to go / some company who share your interests it can provide a sense of security that would quell most of the fears surrounding taking harder drugs as far as intervention of the law is concerned. I'm aware, certainly of people who take hard drugs habitually and it's not pretty, by any means, but the question will always be where to draw the line. Also prohibition of alcohol basically netted criminals a shitton of money, as are drugs now. If you ban something, it just means the people willing to circumvent those bans start making money.
I'll keep this next bit short - do you know what they call alternative medicine that's been proven to work?
Medicine.