So, say you have some money. All things being equal, you'd like to keep it. There are some other things that you like. Food and shelter and video games and such. They cost money. So you have a trade-off. You like milk and you like $1.99, but you'd rather have the $1.99, so you buy the milk. Your preference for $100 probably exceeds your preference for a jug of milk, so you probably won't purchase. You also probably won't purchase sour milk, even at $1.99.
Your response to these trade-offs is to set some guidelines. When spending money on a thing, you want to spend the smallest amount possible. When evaluating a thing for possible purchase, you want it to be the best thing possible. If the thing is expensive enough or low enough in quality, you don't make the trade.
Now imagine that you were a legislator who liked freedom. All things being equal, you'd want more freedom rather than less. When crafting a law, you'd want to make sure that law restricted freedom as little as possible while providing the most benefit possible. If it later turned out that the benefit didn't match the cost, you'd repeal the law.
I was just thinking about the semi-prohibition of pseudophedrine, one of the few drugs that I might hope could address a persistent congestion problem of mine.
I can purchase the stuff, but only at a few places in my area, only by giving up my name and address, and only in small quantities. Alternatives are poor substitutes. Many companies don't want the hassle of selling it, so competition is lower. Combine that with the lower counts and it's relatively more expensive then it was before the ban. That's the restriction-of-freedom side. I can't get it as easily, in as high a quantity, or as cheaply as before. Likewise, stores are less able to profit from selling it.
The reason for the restriction of course was the prevention of its use in the production of meth. The disadvantage of meth is that people use it and then get addicted and then get unhealthy and jobless and steal shit to buy meth (of course some of the worst externalities come from the fact that it's illegal - the cost is higher so more things must be stolen, and those producing, selling and consuming must engage in naturally dangerous black market activity). Anyway, the idea is that we trade some freedom in return for less meth.
Well, that's the theory, but have the legislators shown their work? Has anybody studied pseudofed restrictions to confirm or deny that they have a significant affect on meth production? What were the results of those studies?
The same question could be asked anywhere... How much safer are we now that the TSA has banned water? How much healthier are residents of cities that have banned trans-fats?
Are we buying sour milk? If we knew we were intentionally buying sour milk, it would show that our legislators don't care about freedom at all. If we buying sour milk unintentionally because we weren't checking before or after buying, well that at least suggests that they don't care that much, do they?