Avira, there are many cases in gemora when amoraim recommended or not certain foods, that were not necessarily obvious. I am not bringing examples because I presume you would agree. That means that it is not a mayla to rely on ignorance when one can learn better.
Smoking probably was not a noticeable problem before public health and antibiotics. Before that, people were dying from bacteria and, in cities, from spoiled milk. Smoking was considered healthy from 1500s to 1850s and tobacco has actual effects in attention enhancement (nicotine itself) and some anti microbial and anti fungal substances.