Yes it would need controls and yes there would be abuse as there is with alcohol and tobacco, however there are plenty of arguments for legalisation that include health, economic and social benefits.
* Better informed decision making including those pertaining to people with latent mental health issues that could be exacerbated by drugs/alcohol
* Massive tax revenues that could be diverted to education, control and where necessary treatment.
* Job creation in the drugs industry - leading to further tax revenues
* Elimination of impurities due to the current practice of cutting for profit. Many argue that the crap they cut drugs with does more harm than the actual drugs.
* Dosage control to minimise the risk of overdose
* Undermining the main income of organised crime
* Reduction of street, gang crime and robbery
* Transparency
* Huge savings for the judiciary and prison systems
The issue for cannabis is that it remains in the bloodstream for a month so at what point are people fit to e.g. use machinery given that they are no longer stoned after a few hours? The missus employs construction apprentices and they are tested monthly - that would have to become widespread practice in the workplace.
Drugs carry huge risks for a small percentage of the population (more people die in the uk falling off horses than cannabis, ecstasy and LSD use combined for example) but if those risks can be further reduced by legalisation and the cost of legalisation is more than covered by the income generated and there are other benefits in terms of crime reduction I reckon we should try to overcome historical prejudices based on disinformation and exceptions to the rule and give it a go.
As regards the money - which we'll need post-Brexit - California is looking at an annual tax income (cultivation tax and retail tax only) of $2 billion this year rising to $4 billion by 2020 - and that's just one state and for recreational use only. On top of that there's a whopping $6.27 billion expected from medical marijuana sales by 2020. Then there's are massive savings to be made on the judicial system in terms of prosecution and imprisonment, additional income tax and jobs. Nevada reports that 40,000 jobs can be supported by the industry in their state.
The downside of just legalising and regulating cannabis and not all drugs is that the Mexican cartels are attempting to replace their lost income with increased poppy production for heroin and I guess if we regulated everything, criminals would still be criminals and would move into something else when their money dried up. But drug money is huge and I feel it's better spent on supporting our society rather than undermining it.
Just read a (reputable) survey that shows that whilst only a third of Brits admit to having taken illegal drugs, 52% are in favour of legalising cannabis providing the controls used in America are applied.