What I think, e-cig is not bad, same as mild coffeine drinks like cola or drinks with extremely low alcohol like kwass in Russia or non-alcoholic beer or vine.
The bad thing is that we copy the worldly lifestyle. In my country we have a big bunch of missionaries. When they make photos, I've seen some them showing some gang signs. Like it's cool. The words "gosh" and "heck". The washable tattoo stickers for kids... That makes me sad, because that looks for me like from the Lehi's dream, - people that have partaken of the Fruit of Life, and now look to the big and abominable building with longing on their faces...
There are many things that technically can not and shouldn't be forbidden. But if we stick to them, we may make more serious mistakes. If it's a bridge we do not want to cross, there's no need standing on it, right?