Re S. divinorum.

First, to reiterate what a lot of posts have said: Salvia is not like marijuana at all. It's a shamanistic drug, not a party drug. If someone were not prepared for it, they could be terrified (I had an out-of-body experience on it, which I found fascinating but not exactly pleasant).

Like any drug, it isn't idiot-proof. I suppose, because of salvia's overpowering effects, there is some danger (of the falling-out-of-a-window variety). The greatest danger, though, would be to the ego of an unprepared teenager. Our society seems intent on making everything as idiot-proof as possible, and thus ruining the fun for the rest of us. I can't deny some amusement at the thought that idiots who want to get high are smoking this stuff unprepared, and getting a far different experience than they expected! This brings me to the point:

Level-headed people should advocate a culture of legal but respectful use for drugs like salvia, psilocybe mushrooms, etc. These drugs are very safe when used in very specific conditions, but it's up to the user to ensure that. In this way, they are similar to firearms. You wouldn't give a kid a gun without preparing him to use it safely. You could argue that guns should be more restricted, but in the hands of a responsible, well-trained person they are safe, and our gun laws reflect an assumption of responsible use.

The analogy falls apart, however, when one considers the relative danger of drugs and guns. We allow people to possess machines with incredible destructive force, because we assume (sometimes in error) that they will handle them responsibly. Nobody ever killed ten people with a psychedelic mushroom! If we can accept the inevitable misuse of firearms, then we should accord the same leniency to psychedelic drugs, which are far less dangerous by any measure.