Would people still smoke cigarettes if they were not addictive

Yes, indeed they would. Besides the well-known physiological dependence that we have for nicotine, there is a significant behavioral component to why people smoke cigarettes, tobacco pipes or cigars. Tobacco manufacturers have made a huge fortune on the pleasure that many people derive not only from the physiologic effect of the chemical upon them but they also describe enjoying the "rituals" associated with holding and puffing on the cigarette, they enjoy the pleasure of drinking alcohol whilst smoking as well. Some pipe tobacco smokers enjoy simply puffing on the pipe even when there's no tobacco in it, in fact. Such people commonly report that they experience a calming sensation just from this, interestingly. The addictive nature of nicotine in addition to the "ammonia chemistry" which was employed by cigarette manufacturers in an effort to hasten the euphoric effect that the product had was a "bonus" for these companies to enhance how well their product sold.

Please note that I do NOT advocate the use of nicotine-based products for children, adolescents or adults. I'm simply offering my comment on this issue as best as I understand this matter.

They probably would smoke anyway. I mean there has to be a reason they started in the first place... right? It would probably be easier for them to quit though.

most likely because it 'relaxes' them. but they would be able to quit when needed

I smoke because I enjoy it.