natural tobacco:cigarette tobacco::hemp:cultivated marijuana
the natural tobacco plant is about as harmless as any normal non-woody plant if combusted and inhaled. there are many differences between the strains of natural tobacco and what you find in your cigarette, much like there are many differences between a natural hemp plant and one grown to maximize thc content.
the cigarette tobacco you smoke every day has about 1000 years of selective cultivation (breeding) behind it. this kind of tobacco is bred to contain much much more nicotine than natural tobacco or even tobacco used by the native tribes that inhabited the americas before the white man showed up. the same thing goes for hemp, except hemp might have close to 4000 years of selective cultivation.
tobacco isn't a bad thing, per se. you can smoke natural tobacco or tobacco bred to contain more nicotine with very minor health problems (compared to regular cigarette tobacco). the problem with smoking cigarettes provided by Big Tobacco is that all the tobacco has gone through massive hereditary engineering.
there isn't such a thing as "tobacco is bad" or "tobacco is good". tobacco is both bad and good: it all depends on how much you know. go educate yourself.