As a member of the Scandinavian countries who are your supreme overlords, I have come to expect that our government tries all it can to keep it`s population healthy and tells us the truth when it comes to subjects of drugs. And I trust those who can put me in jail a lot more than the an who can get me into jail.
While Scandinavian policies in general are more evidence-based than the US's (and most everywhere else's), you have to understand that this is a fairly unique issue compared to other civil liberties due to the fact that there are multiple international treaties from the 60s and 70s (in particular, the Single Convention on Narcotic Drugs and the Convention on Psychotropic Drugs) that your country is party to. This makes it a lot harder for more progressive nations to make changes based on new evidence due to the significant power other UN member states hold. Countries with government-regulated stores for buying weed are technically in violation of both of the treaties I linked, but everyone is mostly looking the other way with that since all the experiments with it have turned out to be positive.
There's also the issue that politicians are forced to appeal to their uninformed (about a lot of issues) constituents' emotions, oftentimes with things directly contrary to the available evidence, if they hope to win elections. Nuanced and sometimes unintuitive solutions to difficult problems usually sound less appealing than simpler, straightforward ones--at first glance, legalization and regulation of everything to reduce the negative impacts of drug use sounds stupid and potentially disastrous, but data from Portugal, US states with legal marijuana, alcohol Prohibition in the US, the steady worldwide rates of drug use regardless of legality or penalties, and South American countries' plague of organized crime strongly suggest that it's a better option over the status quo.
Actions have consequences. Outside of reasonable use, drugs, even weed, can affect other people negatively.
Those actions are what should be criminalized.
However, someone high on drugs while driving have slower reaction times, or impaired thinking, or compromised vision etc. which endangers other people on the road. That is ONE example obviously.
However, alcohol does the same thing and is legal, though its illegal to drink and drive (talking about the US here specifically). So then one would say well then make weed legal to and just make it illegal in the car like alcohol.
Now my counter-argument would be that its quite hard to test for drug levels like a breath test since you'd need to take a blood sample I'd assume. But assuming that there is available technology to test for it like alcohol, then fine. If you want to do it and there are laws in place just like alcohol then fine.
Oh, don't get me wrong, intoxicated driving should absolutely be illegal. Simple DUI penalties in the US are a joke for how dangerous it can be. I remember reading an article about a weed breathalyzer, but I'm not sure how that's coming along although it'll certainly happen eventually since it's feasible and there's a market for it. Even without that, field sobriety tests are pretty accurate when it comes to determining whether or not someone is dangerously high on something, and failing them without testing positive on whatever breathalyzers are available would probably be good enough for a field or station blood draw.
But it all comes back to what I said. Why? Why do something that IS bad for you. Maybe not that bad, maybe you won't notice it for years, maybe no one else will ever get hurt with it, but why? Why not do something else, something safe, something healthy? Why?
In the end I am okay with regulated legalization of some drugs such as marijuana, but I don't support it. I think drug use for non-medical reasons is bad and stupid. But as long as there are laws in place to still protect people, I guess I have no right to stop someone else from screwing them self up alone. But the second they hurt someone else I'll be calling for justice and looking to punish them. So for yourself and others, why do it in the first place?
Its all a very complicated topic, and hence its one I usually stay away from. Ah, off-topic forum. ^^
EDIT: This is a bit of me rambling. I see the points on both sides and therefore I see the topic in many shades of grey. And when you add to the equation all the other kinds of drugs, meth, acid, etc, it gets even more complicated. And beyond all that I don't understand the point of hurting your health for a "high" when then are so many other healthy ways.
That's the thing though, people are always going to use regardless of legality. The current system is making criminals out of people who haven't hurt anyone and is perpetuating a cycle of violence and poverty. Someone who can't get a job because they got busted with drugs doesn't have many options, so a lot of the time the only way they can make money is to sell or get involved with other illegal activities. This was especially bad before the Fair Sentencing Act in 2010 since crack (a drug most popular in low-income areas) had federal sentences equivalent to 100x its amount in powder cocaine (a drug popular among middle class and up users with more options to begin with).
Thinking it's stupid is perfectly fine, but deciding to force that view on others by making them criminals isn't. That's the main issue here; it's not whether or not drug abuse is harmful (it is in most cases), but whether or not the government should be our moral police, and more importantly, whether or not the significant harms from the War on Drugs are acceptable collateral damage for accomplishing basically nothing.
LSD, and most other hallucinogens for that matter, are actually some of the most benign drugs:

The reason meth, heroin, crack, and other drugs like that should be legalized is because they're so dangerous. Right now there's no way of guaranteeing the consistency and safety of a substance--not only do users have to worry about possibly ODing due to the purity varying hugely between purchases from cuts, but they also have to worry about their drugs being incorrectly mixed with something far more potent and killing them that way too. Low-purity heroin is sometimes combined with cheaper fentanyl or fentanyl analogues, which are extremely strong opioids 10-100,000 times more potent than heroin by weight, and it's virtually impossible to mix those in without getting hotspots that are drastically more powerful than heroin alone. Even LSD on its tiny blotters isn't immune to adulteration since 25I-NBOMe, a psychedelic active in microgram ranges which has hardly any history of human use and is relatively easy to fatally OD on, is often substituted for profit. Guaranteed purity from similar regulations to the ones currently used for pharmaceuticals would solve those issues, and it'd ensure sterility too.
Edited by JeffMagnum, 01 July 2015 - 07:05 PM.