It is true that a drop of pure nicotine can be deadly, and that if you concentrated the nicotine from a pack of cigarettes (or a can of snuff, or a box of pharmaceutical nicotine products) and put it into your body all at once, it would likely be fatal. But, again, so what? Nicotine users are never exposed to pure nicotine and never take in that much all at once. If you took your typical day's worth of food and stuffed it in your mouth all at once, that would probably kill you too, even though it would be harmless if you took the usual time. This may seem like a silly analogy but it is no more silly than saying that a huge dose of nicotine, delivered all at once, would be deadly. Neither one says anything about the safety of normal use.
Keep in mind the saying from toxicology: "The dose makes the poison." Enough of anything, delivered fast enough, is deadly (including food or water). For many medicines you have on your shelf, ingesting the entire bottle at once would be deadly.