There is no way Heroin or Meth can be "used recreationally" without causing self-destructive harm and affecting all of society.
Drug addicts take drugs. They're not deterred by the legal status of the drug. Heroin being illegal doesn't stop addicts taking heroin.
By making a drug hard to get illegally all you do is make a drug addict commit more crime to get it, or take more risks.
Heroin users inject contaminated drugs, using re-used (sometimes shared) needles, in dirty surroundings. This carries considerable risk of infection from diseases like hepatitis and HIV. It also carries significant risk of abscess or even amputation.
Heroin users need money to buy heroin. This money can come from sex working. Sex work is an unregulated semi-legal activity. There are risks of rape and assault. There are risks of sexually transmitted infections. People dislike the advertising associated with sex work. Because sex work is unregulated there are other vulnerable groups dragged into it - trafficked women, homeless people, and children.
Or the money comes from other crime - mugging, burglary, theft. And people spending all their cash on heroin will steal food.
Heroin's illegality means that its supply is controlled by criminal gangs. There is violence associated with these gangs.
Even the "nice" drugs - cannabis - have considerable problems from their illegal status. We can't do proper science because of the problems of getting and giving cannabis. Cannabis is sometimes grown by slaves trapped in grow-farms in houses. There are links between cannabis grow farms and housing benefit fraud in the UK.
Heroin being illegal makes it harder for people to look for or get help. We can't taper addicts down using heroin, so we use methadone. It's tricky to talk about how addictive a substance is, but some people feel that methadone is more addictive than heroin.
When heroin is too tightly controlled you just switch addicts to even worse drugs. See, for example, the Russian drug Krokodil. This is desomorphine, cooked from codeine-containing meds, but in dirty unclean situations. The high from desomorphine is intense but short-lived, so people cook and cook frequently. They're careless with the procedure. This means that they're using filthy needles to inject god-only knows what. An image search for "krokodil" returns many grisly horrific images. Addicts using krokodil live for about 3 years.
Also, Krokodil is... well, it's barely desomorphine. A RP/I reduction of codeine... that certainly doesn't produce what they want it to (except in tiny, tiny quantities perhaps, more as a side-chain reaction though).
Also, just to point out, a lot of the Krokodil images were mislabeled from another drug (that I can't remember) -- it's horridly dangerous, it will kill you, but it doesn't eat the flesh of your bones like is commonly reported, unless you're shooting acetone. And trust me, you know if what you're shooting hasn't been cleaned properly -- that shit hurts like fuck, and definitely ruins any "high" you might get. *shudder
You'd be surprised.
I am an ex-heroin addict, and I will say that I certainly DON'T fit into the "doesn't cause harm" basket. I fucked things up well and truly.
But for every addict, there are a surprising amount of "weekend warriors" who dabble here and there and never get drawn in (for a variety of reasons).
Unfortunately, I was not one of them, even though at the time I thought I was. That is the danger.
The argument is: "These drugs are unsafe, therefore they should be legal because making them illegal makes things even worse."
Society can hardly intervene in every individual's self destruction. But it cannot allow drugs which are not useful for anything BUT self destruction.
This is why drugs are complicated and different. Blanketing all "drugs" as bad while drinking Coffee, Whisky and Aspirin is just hypocritcal and dangerous.
[1] http://en.wikipedia.org/wiki/Methamphetamine#Pharmacology
http://www.ncbi.nlm.nih.gov/pubmed/22289608
Also, as an anecdote, I have received d-amphetamine by prescription and have taken Desoxyn about five times. They're not that different, Desoxyn is subjectively 'cleaner'.
I stick to caffeine though, and roughly half a Modafinil every two weeks. Amphetamine is just not my friend. Your mileage may vary.
Why not? Should I not be permitted to destroy myself if I so choose?
You've stated the government's position exactly, and they can provide some helpful additions to your list of dangerous drugs.
Methamphetamine is legal by prescription. This is the war on drugs in its truest form: giving well-connected businesses (like big pharma) special advantages at everyone's expense.
And they have the absolute fucking audacity to call it "Marinol".
Please read up on diacetylmorphine maintenance programs. There is copious literature on this.
Laudanum was used safely for the better part of the late 19th century. The word "heroin" is actually a trademark of Bayer (yes, the same folks who also gave us "aspirin")[0]. It was sold successfully and without any large-scale devastating effects for several years; the reason it was eventually outlawed had nothing to do with any negative repercussions of the drug on a large scale.
As for methamphetamine, according to the MTF and NSDUH studies, the majority of people who have used methamphetamine in the last 30 days do not meet DSM criteria for substance dependence[1]. That's not looking at everyone who's ever used methamphetamine; that's looking at people who have used it within the last month. Clearly it can be used "without affecting all of society"[2].
This is, of course, ignoring the fact that methamphetamine is Schedule II and can be obtained legally (albeit in rare cases) with a prescription (under the brand name Desoxyn).
[0] Both trademarks are now generic; Bayer eventually lost these trademark protections. This is why your local drugstore is allowed to sell acetylsalicylic acid under the name "aspirin" (with a lowercase "a").
[1] Most also wouldn't meet the DSM criteria for substance abuse either, except for a technicality in the criteria that references the legal status of the drug, which is naturally self-fulfilling.
[2] Unless you are looking at the economic impacts (ie, Nicaragua 30 years ago, North Korea and Afghanistan today, in which case you have a point, but that only serves to emphasize the need to short-circuit these black markets with legal ones).
Prohibiting substances will never stop users from seeking them out. It will however make their use less safe (contamination, mislabeling, inconsistent purity, dirty needles, hesitance to seek medical attention for fear of prosecution, lack of available research on currently illegal substances hindering treatment of overdoses, etc.) and create a black market around the distribution of those substances (leading to violent crime, overflowing prisons, traumatized neighborhoods and broken families, etc.).
If fact, all of our available evidence from countries that have decriminalized hard drugs points to a reduction in abuse. That's just intuitive to me... wouldn't you be more likely to relapse if you were a felon unable to find gainful employment? Or a mother whose son just got shot for pushing crack on the corner? The repercussions of breaking up families, criminalizing and incarcerating our most vulnerable members of society, and exacerbating violence in our poorest communities cannot be understated. The drug war has caused a whole plague of societal ills, one of which ironically appears to be higher rates of drug abuse.
For those that would, having to go but it from some non legitimate source where they are potentially exposed to non-pure product and potential crime certainly isn't going to help their situation.
Let's be clear here: a legal prohibition is nothing more than an ultimatum. It's a threat of punishment - "if you use heroin, and we catch you, we will lock you in a cage".
If you're opposed to people using heroin because it's harmful, can you explain how making people serve prison sentences and have life-long criminal records in addition to being heroin addicts somehow reduces the amount of harm that they suffer? Because, from where I'm sitting, it seems that the solution you offer to the harm caused by heroin and meth is to do even more harm to people, on top of the harm caused by the drugs.