The War On Drugs is no better now than it was in the 1920's when we called it Prohibition. It turns a mild social problem into a major one, creates crime, and takes people away from productive work. It is a cure far worse than any plausible disease.
If you think that the current crop of illegal drugs are "inherently" going to lead to crime in a way that alcohol isn't, you'll have to explain why Al Capone was a big-time mobster, making a large career out of sneaking around the ban on alcohol, and killing people to do it, but no one does that now.
The War On Drugs is an attempt to prevent people from using some substances that some government officials believe are "bad for them". It does not affect all harmful substances (for instance, alcohol is excluded), and it does not restrict itself to substances which are mostly harmful. (For instance, there are well documented medical reasons for people to use marijuana, and indeed, the objection that got marijuana in as a controlled substaance was raised by people who grew cotton - which makes weaker, heavier, fabric than hemp.)
The War On Drugs is a false merging of a problem (drug abuse) with a non-problem (drug use). It is a false dichotomy between "bad" drugs and "good" drugs. No explanation is offered for why it is okay for doctors to prescribe morphine derivatives, but not okay for them to prescribe marijuana. No explanation is offered for the widespread availability of Ritalin and Prozac, but an absolute ban on marijuana.
The War On Drugs artificially inflates the cost of some products (the drugs which have been made illegal) by creating artificial scarcity, which makes the drug trade very profitable; profitable enough for people to kill over. How many people have been killed in turf wars over aspirin?
The War On Drugs has created an incentive for the authorities to lose sight of a lot of due process issues, and to villainize people who are doing nothing wrong. (They may be breaking laws, but that has nothing to do with right and wrong.)
My father died after a prolonged illness. He was constantly nauseated, in pain, and dizzy from the "good" drugs doctors were allowed to give him; by all accounts, legal marijuana would have allowed him to keep down, and possibly enjoy, food for the last three to six months of his life, and might have allowed him to better withstand the pain he experienced after his leg was amputated at the knee; instead, he was forced to take "good" drugs which left him deeply incoherent (he sometimes thought he was in Germany), sick to his stomach, and did nothing to change the quality of his experience for the better. He was a brilliant thinker before this, and I, for one, would rather have seen him in good spirits, and a little silly, and possibly even alive and relatively healthy today.
Artificially inflated prices create violent crime; children running home from school are shot by accident if they come to close to a turf war. People whose neighborhoods are inhabited by drug dealers find their property losing value. If drug dealers were businesses like everyone else, this probably wouldn't happen.
Drug tests have an unacceptably high rate of false positives, leading to people losing, or not getting, jobs for bogus reasons; this hurts everybody, not just the former employees. In fact, the former employees may have a hard time getting future jobs as well - whether or not they used drugs, and whether or not any drugs they did use affected their job performance.
Mandatory spot-testing for drugs is a massive invasion of privacy; I for one am not about to put up with it from anyone, even though I am not likely to use any drugs.
Drug dealers and "drug lords" enjoy huge profits, out of line with the quality of goods they produce, and without real regulation to keep them behaving in a responsible manner.
Politicians get big campaign contributions from people who have made a fortune from the War On Drugs.
If it matters (it shouldn't), I am mildly opposed to the use of recreational drugs, because I'm not convinced that it's beneficial; however, I extend this to drinking alcohol (admittedly, I'm a sucker for Bailey's and coffee), and I even avoid headache medicine. I don't think my opinions should constrain other people's behavior.