Your friends might be right... If we were SMOKING or If you only consider the E-Cigarettes that the Cigarette Companies sell, like Vuse. If the conspiracy theories are correct . I'm sure PM is adding the same Addict You, stuff, to their juices as they use in the cigarette. Why wouldn't they, those additives very well might cause cancer.
But the smoke from burned plant matter and additive chemicals is the main cause of cancer in cigarette. I know what chemicals are my Vape juice. So far they haven't been shown to cause cancer when vaporized or inhaled. When SMOKED, some of them, sure. I do vape mostly NET juices, after all.
SMOKE of almost any kind from almost any source can and likely does cause cancer. Except for the occasional dry hit, which can be avoided. There is NO SMOKE from Vaping.