E-Cigs are not for everyone so I don't know whay they would be so worried. Some people will still use the gum and the other items no matter what we say, so why the big deal?
I think there are a really 2 main things going on(As well as financial gain it is a philosophical viewpoint):
The drug companies do not want people self-medicating in any way shape or form. They want you to buy THEIR products. They do see e-cigs as a potentially large enough threat to try to stop it now. Additionally, I wouldn't be at all surprised if, in the not to distant future, coffee and tea drinkers will have to pay $10 a cup or have to buy caffeine patches or caffeine gum.
The other main thing is that the anti-smoking industry has become big business. But beyond any purely financial gain, no matter how well intentioned many anti-smoking advocates may have originally been, IMHO many have become anti-SMOKER zealots. There is no rationality left - hence the fake cough some non-smokers do when they see someone smoking. Psychologically, they cannot even handle the site of someone doing something that even LOOKS like smoking. To these type of people, if you said to them " that quit smoking drug has a side-effect that could kill you" they could say, and think it was completely logical and reasonable, "So what, you're gonna die if you smoke anyway!"