Ok so if I understand your argument correctly you mean that the danger with a drug such as ritalin is that it will be used with the wrong purposes. Which is what happens sometimes, since it regulates dopamine, which is a feel good hormone it can give you a buzz if you take enough. However that is also why the drug is so controlled and why every time you want to get your ritalin from the pharmacy you need a new prescription (the original). This makes your comparison of ritalin to something you can easily buy such as a knife wrong.
No it should be controlled. I absolutely agree. The analogy was merely to attack the bandwagon that people use to justify their opinion of eliminating a product. In fact, I was agreeing with you that people bring it to themselves. And like knives, it ultimately comes down to how it is used.