One could answer this question many ways I'll just answer it as I see fit. Alcohol is a legal drug, that can be easily abused and yet is at the same time perfectly acceptable. And yet this drug contributes greatly to violent crime, crime in general, family welfare and many other issues. It causes deaths, injuries and sorrow. But yet we accept it.
Cannabis on the other hand is illegal in most countries. Yet what medical evidence there is suggests that it does less harm to people's health than smoking or alcohol does. It is not typically known as a drug that causes people to be violent. I'm not saying it does not cause violent but I have never witnessed violence by someone smoking cannabis. I have however, seen those same people get very violent when drunk. It clearly contributes to crime in that the selling, growing, manufacturing of it is all illegal. And smoking it or rather consuming it is typically illegal although it can sometimes be decriminalised if someone is merely smoking a joint or something. Does it contribute to crime such as sexual assaults, theft etc. Probably but its not as easily quantified as that of alcohol use.
Party Pills (Pills containing BZP). These were a common occurence just weeks before now in New Zealand prior to legislation being passed in parliament meaning such pills are illegal. The main concern with these pills were that the BZP in the party pills was dangerous and could cause death and injuries. It was and has been illegal in other western countries for many years but was legal here until recently. There were cases of people being hospitalised and one man having ongoing problems. However, whether these people simply ignored the recommended dosages or not is unknown. These pills were primarily introduced here for people who had addictions to either speed or ecstasy and or provide a safe alternative to such drugs. However, it became far more popular than what was originally thought and it first got restricted to 18 years old and plus. But increasingly there were concerns and laws were passed in parliament.
This however, brings a new problem. As now people consuming pills containing BZP are illegally taking them. Also this saw new drugs introduced that are far more unknown. That could be potentially far more dangerous than the previous party pills and which currently do not have restrictions such as selling to 18+ only.
I don't know anything about whether people taking such pills were likely to become violent or contribute to crime. I do know however, that overdoing them meant not being able to sleep and simply not coping. I know this because my mother and her partner observed my brother and a friend taking it.
The last drug I will talk is commonly referred to here as Pi but may well be called Crystal Meth elsewhere. This drug has been constantly in the news for the last five years. It is a drug that clearly causes crime and in particular violent crime. Multiple murders, child abuse, rape, sexual abuse, physical abuse and the like. Its rather expensive and very addictive. Thus people are stealing cars, robbing, stealing money from businesses, perhaps prostituting and the like just to get their next fix. It is a problem because gangs deal in it, it destroys lives and its something that constantly seems to be a problem. It is the one drug that I seriously do not like and will never like.
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Alcohol can be dangerous, but only if it is abused. Party pills can be dangerous but if taken right should not necessarily cause problems. While, cannabis while illegal is common and is considered largely acceptable by many number of people in the community. I have my problems with party pills, I think they can offer a safer alternative to ecstasy and speed. On the other hand, one can see that its basically condoned and thus seen as acceptable. Alcohol I drink personally, but I don't think its alcohol itself that is the problem but people abusing alcohol that is the problem.
Onto Cannabis. I think it should remain illegal, I have smoked it many times. I think it has to stay illegal not necessarily because its dangerous for your health or such issues. But because you can't be seen as accepting it. However, personal use should be decriminalised (I believe it could be but I am unsure) and the police should much rather concern themselves with the dealers and those growing the drug. As these people can often have other criminal activities going on. As for Pi well its horrible, it is illegal but it looks set to stay.
I did not mention speed and ecstasy simply because I wanted to focus on party pills and pi rather than those. Heroin has never really been a problem here since the late 1980s when a supply line was stopped. And to be honest, there doesn't seem to be that much use of cocaine here either.
Dugs can be bad, some worse than others. But most of the time, its not the drugs themselves but the people that choose to abuse them.