I think that the notion that canabis leads onto other drugs is valid - but importantly, it is not automatic.
People who move in a circle of people who use canabis, move in a circle of people who take drugs, and therefore their exposure to other drugs is obviously higher than average.
However, that does not mean that every canabis user chooses to start using other drugs, and that is where that argument falls down. The inference that one will and must lead to the other is a false assumption, usually made by people who have no direct experience of drugs, and imagine that canabis users get their cannabis from shifty men in raincoats in backstreet pub toilets.
Wrong.
People get cannabis from their friends, and the camaraderie of taking drugs together is a bonding experience.
Turning to the notion of legalising cannabis - i think it is, and always has been, worth trying.
Let's face it, the double standards of our culture - no to cannabis, yes to alcohol, is facile, and the so called 'war on drugs' has singularly failed to make any meaningful impact.
So, as a society, we have to accept that we have a drugs culture, there is no choice in that - only a choice in how we deal with it.
Legalising cannabis is a step in the right direction - it will make a dent in the drug cartels' finances and power.
From society's point of view, we have nothing to lose.
Legalisation need not be for ever more - if it fails in its aim, then the legislation can be reversed, so we can only move forward, or stay where we are now.
The problem for our governments, is that far more voters are against legalisation than in favour of it, so even discussing the idea represents political suicide, so we have a long way to go before the idea is tried out in the UK.