Nicotine != tobacco and is not a known carcinogen. Hence, this is now a moralistic conversation as we are now talking about a drug with health effects similar to caffeine (forbidden by Mormons for example)
Actually, as research continues we are beginning to understand the role nicotine can have with cancer. The link I've shared elsewhere in this thread is a good place to start.
https://en.wikipedia.org/wiki/Nicotine#Contraindications
"The accepted medical position in 2007 was that nicotine itself poses few health risks, except among certain vulnerable groups"