LD50 is entirely irrelevant to this discussion. No one goes to the store and orders 1mg/kg of a substance. When considering acute harm, the relevant metric is the ratio between a typical recreational dose and an overdose. For example, there are very few tobacco servings that contain more than 20mg nicotine. A person is very unlikely to come anywhere near the, say, 360mg lethal dose.
Nicotine is more toxic than tar and other substances, as measured by the LD50; it's just that those substances are all really hot and carcinogenic.
360 mg / 6 = 18, less than 1 pack has a lethal dose of nicotine. However, since uptake by the body is low for nicotine, smoking what would seem to be a lethal amount doesn't kill people.
