Nicotine is "toxic" in the sense that the absolute dose needed to cause injury or death is quite low, but assuming there is no potency variation due to quality issues (as seen with street fentanyl), this doesn't really have any relevance in regards to how acutely "dangerous" or "harmful" nicotine is. The therapeutic index is the correct gauge to use, and I doubt that nicotine's therapeutic index is all that different from that of caffeine. When's the last time you heard of a tobacco smoker dying of a nicotine overdose?