My common point when it comes to these factors is even if you strip away my moral reasons for drugs legalisation the current prohibition is illogical, as it doesn't look at the relative harms to society or the individual, merely keeping alcohol legal because it's currently legal.
"Estimating the true relative harms of alcohol and cannabis is not easy as there are no societies today where the two drugs are equally available. However where neither are legal – as in some Islamic states – alcohol appears to cause more dependence than cannabis, even in Morocco a traditional cannabis growing country."
Yes it is hard to completely compare legal and illegal drugs (that reminds me of the conversation Mr Nutt said he once had with Jacqui Smith as I mentioned before) but that doesn't mean that the comparatives shouldn't be looked at. We all see the damage that alcohol does to our society, I think the most underestimated thing about drugs legalisation would be the positive externality of reduced alcohol intake.
The only bit of this post I don't like is the start:
"I am often asked the question “if cannabis was as freely available as alcohol how many would use it and would its harms increase?. Of course the answer is yes to both."
That answer doesn't appear to answer the question - I think it should have read would usage increase and would harms increase.
I don't know how you can say harms would definitely increase, given that as stated in his post the Netherlands has one of the lowest cannabis usage rates amongst young people.