Should've said certain drugs really, only caught the arse end of the news, Cannabis was mentioned. I don't think any of the rubbish should be legalised, personally I don't agree with any of it.
Alcohol causes much more damage "pound for pound" to the body than what cannabis does, and that's before we include the people who end up in hospital because some drunken idiot decides to shove a glass in their face.
If cannabis was really that bad, then I doubt for one minute my doctor would have told me to "smoke as much as I can" in the 9 months leading up to my surgery last year.
I personally see no problem with cannabis being legalised for use in the home, and at the current street rates (£20 gets you 1.6 grams) the government could make a killing overnight with the tax.
Alcohol may well cause damage as well, and I agree it's no good really either. However a good friend of mine after being on cannabis for years turned into a completely different paranoid bloke, constantly having panic attacks and feeling like a fruit loop. So yes, I do see a problem with it being legalised in anyway shape or form.
The real problem imo is the strength of what is smoked.
Some people have been smoking dope as a way of relaxing or in a social gathering for years with no ill effects.
Then again, a very good mate of mine from my school days who has used it since we was kids is totally oppsed up because of the amount he has smoked over the years.
He, as most users started off will a spliff or 2 on a weekend with his mates.
As cigarettes became more expensive, he started to roll his own. Soon it became too easy to slip a little dope in there. Next came "skunk" 
Nowdays, he has gone from the kid that everybody at school wanted to be too the kid from school that everybody avoids like the plague 
Sounds like you went to school with my son.He used to be a bright,intelligent,sociable kid who had a very bright future ahead of him,and had girls falling at his feet.Then he discovered Cannabis.He argued that it was his choice of cigarette brand and it was unfortunate that it happened to be illegal etc.
After a couple of years,he was like a zombie,his education was ruined,all his friends were gone,he couldnt even speak to a girl,and his brain was fried.
I used to spend my nights driving round looking for him,not knowing if he was dead or alive.He attempted suicide by various means and was disgusted at himself that he couldnt even do that properly.He cried in my arms like a baby one night,and confessed that the stuff had f****d his head up completely.I thought the stress was going to kill me tbh.
He got to a point where he was so withdrawn I thought I had completely lost him,and I was sure he would succeed in killing himself in the near future. It broke my heart into very small pieces to see my own child like that and to feel utterly helpless about it.
I had a long chat with him one night,and although I dont remember what I said, he later told me that I saved his life that night,and he stopped taking drugs.
Almost 10 years later he is a really lovely bloke who you couldnt dislike if you tried.But he still has major issues with most social situations,and pretty much lives in his bedroom,so a certain amount of permanent damage was done.
I have spoken to medical professionals who say that mental health units up and down the country are overflowing with people who,s brain have been fried by cannabis use.It doesnt affect everyone like that,but no-one knows in the early days of usage if it will affect them or not.So they (and the people who supply it to them) are playing russian roullette with their own sanity,and ultimately,lives.
Legalise it - no. Shoot the suppliers in front of other suppliers - oh yes.