Historically, nicotine has not been regarded as a carcinogen and the IARC has not evaluated nicotine in its standalone form or assigned it to an official carcinogen group. While no epidemiological evidence supports that nicotine alone acts as a carcinogen in the formation of human cancer (on the contrary, a mechanism of urinary excretion of nicotine metabolites was identified as the link between smoking and bladder cancer [73]), research over the last decade has identified nicotine's carcinogenic potential in animal models and cell culture.[74][75] Nicotine has been noted to directly cause cancer through a number of different mechanisms such as the activation of MAP Kinases.[76] Indirectly, nicotine increases cholinergic signalling (and adrenergic signalling in the case of colon cancer[77]), thereby impeding apoptosis (programmed cell death), promoting tumor growth, and activating growth factors and cellular mitogenic factors such as 5-LOX, and EGF. Nicotine also promotes cancer growth by stimulating angiogenesis and neovascularization.[78][79] In one study, nicotine administered to mice with tumors caused increases in tumor size (twofold increase), metastasis (nine-fold increase), and tumor recurrence (threefold increase).[80]

Christophe
I don't know about an ethical dependence, but nicotine was used as a pesticide in agriculture in years past. So i don't know if long term dependence, either ethicla or unethical is really healthy.