What is the negative impact on someone's spiritual health who uses chewing tobacco?

I suppose you: could make a case that "defiling the temple" (Biblical reference) is not in God's plan, so in that sense, introducing tobacco is bad. But, practically, nicotine won't stop you from worshipping, praying or meditating (might slow down the latter because of the stimulation effects of nicotine). I'd worry more about the hazards like oral cancer or other mouth disorders.