Well chewing is not good for you,but,if its not,its because of the things they put in the tobacco,probably not the tobbaco itself so much,and the fact that you put it in one or two spots in your mouth over and over again,rubbing/chewing on it. Anybody who rubs copenhagen can tell about calluses on their lips and red/white spots on gums etc. You could probably rub spinich with those additives and get same result.Too much of anything will kill you.
Now smoking is not natural,if you are outside around a fire and smoke drifts your way,you'll move.
But all this talk of chewing causing cancer is overblown as far as I'm concerned,I believe we all have the cancer gene in us,but somes might be triggered by chemicals of some kind,some might be triggered by beer,electric magnetic field, smoking,etc,and some rubbing snuff. Thats why you find old men and woman who have smoked for 60 years and still kicking,and old men[generally] who have rubbed or chewed for 60 years and still doing it.If it for sure caused cancer,than they wouldn't be here.
Like skin cancer,I had a spot of skin cancer cut out between my big and next toe,melanoma,not precancer or such. Now my feet ain't seen the sun in 30 years probably,and even back when they did,it was BETWEEN MY TOES! But the sun[they say] causes skin cancer for sure.
My thoughts on cancer,its like aids,if they knew what caused it,they could cure it,they don't really know how it starts,they just see it after it is there. Somethings that you can do after years of them studying it, seems to contribute to certain cancers,but....