This like many laws built to restrict access to products is a simple issue of trade off, it's trading the freedom from responsibility for another freedom, in this case it's freedom from the responsibility to make informed decisions for (yourself/your children) and the responsibility of teaching your children to make those decisions themselves, in exchange for the freedom to actually see the product you want to buy on the shelves of the store and the freedom of the store owner to carry and display products in the manner they wish. In some places pornographic magazines cannot be displayed on shelves, in others they must have a plastic bag which obscures the actual magazine. Again it's freedom from the responsibility of having to explain and discuss it with your own children, in exchange for the freedom to diplay it in a store.
Unfortunately, it is also a case of out of site out of mind mentality. Simply because a product is not visible does not mean it does not exist, measures like this only serve to create further issues, because once the product is available (in both cases here at 18 years of age) consumers are suddenly able to acquire something that all they know about is that it is a hidden secretive product, reserved for adults.
The actual solution is to bring back accountability both as individuals and as familial units. When I was young I lived on base, my dad was Air Force. My father was my sponsor. This means he assumed responsibility for my actions on base. If I did something illegal on base. I was charged as a juvenile offender, and my father was called in in front of his commander and chewed a new one. Then he came home and I was chewed a new one. As a result I didn't get caught doing anything illegal.
It's all about education...but we can't just rely on the schools for that, after all they are not the real world.