Do you think the government should be in the business of defining all manner of victimless crimes? Does it do a society good to have victimless crimes, crimes against the state?
Let's ignore for the moment that these drugs can cause delusions, psychosis, paranoia, aggression, impaired judgment, and homicidal rage. Let's ignore that they're prone to overdoses (society's cost: more emergency calls, more hospitalizations); they cause immense stress on the heart, liver, kidneys; they collapse veins and arteries; they literally eat away flesh in the stomach, sinuses, and dermis (society's cost: more healthcare, more hospitalization, higher insurance premiums). Let's even ignore that they can be used for everything from date rape to cheating at athletics/academics to temporarily suppressing all fear, pain, and guilt.
Let's look exclusively at the costs of addiction to these drugs.
Foremost, there's the financial cost. The addict needs more and more of the drug to get high, hence he requires increasingly large sums of money. It starts with money he has, then money he borrows from lenders, then money he extorts from friends and family (until he's bled them dry too), then petty theft, then violent crime, then anything at all necessary, assuming he doesn't die at some point during the process.
Who are the victims here, besides the addict? Families, friends, the people who have to watch him self-destruct, the people who have to scrape him out of his own vomit off the pavement. There's also the people he robs, the creditors he defrauds, the people whose paycheques are raided to pay the law enforcement officers, court officers, social workers, and EMTs who spend countless hours dealing with the mayhem he causes. I dare you to work at a drug rehab clinic for a month and come back opining about "victimless crimes".
Then there are the human costs. The addict can't hold down jobs at length. He can't produce anything, or better his society while addicted. He can't function. Walk into an addict's place of residence (if he has one), you'll see a piece of property totally destroyed. If a landlord is lucky, he'll be able to evict the addict before he's rendered whatever space he's living in permanently unlivable. There's another dare for you: tour a drug addict's apartment, then tell the building owner drug abuse is a "victimless crime".
But the addict on the street needs to eat and live too. Hence tax dollars feed him. Charity clothes him. He can always find a place to urinate, defecate, and dispose of his trash; taxes will pay to clean it up (hopefully). He lives like this indefinitely, bleeding government coffers dry until either until his dwindling prospects of rehabilitation come to bear or he dies. Rehabilitation is an escape for the lucky few, but like everything else related to addiction, it's expensive and taxpayer funded.
Once an addict is rehabilitated, is the nightmare over? It's unlikely. Drug abusers have a fearfully high rate of recidivism. Even when they do stay on the straight and narrow, they now have to contend with the long-term mental and physiological effects of hard drug use, which begin compounding with the very first use. Depression, damage to memory and concentration, anxiety, paranoia (something I personally witnessed with a friend), crippling headaches, nerve pain, dementia, cancer, ... . I could go on forever, but you can look it up on any addiction resource online. If an ex-addict can't cope and can't work, then even having beaten the addiction, he's society's burden for the rest of his life.
In conclusion: if we lived in a world where everyone existed in their own bubble, not interacting, paying taxes, paying insurance premiums, owning property, contending with crime, etc., and if we didn't count users of hard drugs as 'victims', then indeed we might regard hard drug use as a victimless crime.
We do not live on such a world. I, for one, am content with governments acknowledging this in our laws.