After wandering a bit on your link, I came across the following:
"Unfortunately there is little room for error before the effects become potentially dangerous. When the dose goes above 500 - 1000 mcg the effects can be very alarming, I have seen several people get up and lunge around the room falling over furniture, babbling incomprehensible nonsense and knocking their heads into walls. Several people have tried to wander out of the house. When the experience is over they have no memory of any of this. In fact they usually remember very different events. To an outside observer people in this condition have a blank look in their eyes as if no one is present (and perhaps no one is). It is also common for people to have a facial expression which is probably best described as being like that of a frighten ed animal. It appears that at these "larger" doses one completely loses awareness of, and control over, the physical body and for some reason part of the brain causes the body to get up and move about recklessly while the individual has no awareness of where their physical body is or what it is doing. It seems inevitable that one of these days some careless person will do too large a dose without a sitter and will wander out in the street, or hurt themselves in some way."
The problem with keeping such a substance legal, and available to the public, is that the average member of said public, especially if he or she is young, is bound to overdose on this plant. As you can see above, the results are potentially catastrophic.
That can happen with almost any drug.