I could have written my sentence better. If I used illegal-ness as my main qualifier instead of harm, that might fix some confusion.

And, it is amazing that the most illegal drugs are the least physically harmful. Still not perfect, but an improvement.

I'm no expert on this, so I admit that this might not always be the case. I went out looking for something to illustrate my point. Didn't need to go any further than wikipedia: http://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Rat...