"He strains to hear a whisper who refuses to hear a shout." -Robert Jordan
In essence, getting upset at them is only going to make them dig their heels in further. Now, I'll grant that many people, especially older people who are set in their ways and feel like they've earned the right to tell the rest of the world how to live, simply won't listen to reason no much how honey you cover it with. But If anything has a better chance of working, it's approaching them in a friendly manner and asking them if they'd be willing to learn the difference.
The problem is that the vast majority of ANTZ (anti-nicotine and tobacco zealots) think that nicotine is the real demon in cigarettes -- which isn't their fault as it has been bandied about for years in the media that nicotine is what makes people addicted to cigarettes and is therefore the only thing that's really talked about at any length. A gross oversimplification, but that's what the media is best at. It's important to tell them that they're correct in the sense that, yes, nicotine is harmful, but it's arguably more important to inform them that, of the thousands of other ingredients in cigarettes, it's also far more benign than most of them. Nicotine is a stimulant and a vasoconstrictor and it has addictive properties, so that's not particularly great. At the same time however, caffeine is very similar and shares the same properties, including its addictive properties. The difference is that most people don't consume nearly enough caffeine-laden beverages to become addicted to them. But if you demonize one, you must demonize the other for the same reasons.
People must be made to realize that E-cigarettes have stopped you from smoking regular cigarettes, and in so doing have also stopped you from polluting yourself and those around you with the thousands of other toxic chemicals in regular cigarettes, because E-cigarettes don't contain them. (Well, they do in tiny trace amounts, but that's not important and there's no point in giving them something negative but inconsequential to latch on to.)
Maybe -- maybe -- kindly trying to inform them might help matters. But if they refuse to listen to reason, there's really nothing you can do. For some people, their own beliefs in the world can be just as firmly entrenched as a highly religious person's faith, and there's no reasoning with that.