Look, I'm not going to sit here and say that we know enough to conclusively say that e-cigs are generally "safe". But the studies thus far are mixed at best.

Here's a study which compared (in vitro) the toxicity of e-cigs and tobacco : http://www.mdpi.com/1660-4601/11/11/11325/htm

it finds "no cytotoxic, genotoxic, or inflammatory effects".

Now, the nanoparticles aspect is not something I have delved into deeply, but the reports of metals in your eliquid where attributed to the cartridge, rather than the eliquid itself by one of the authors of one of these studies: https://news.usc.edu/67718/e-cigarette-smoke-found-to-contain-toxic-metals/

Which, of course it would be nice to avoid. I personally would like to see some manufacturing standards brought into action in the U.S. I'd love to hear someone chime in about the nano-particles issue mentioned in the paper. My impression was: very small particulate is very dangerous if it is something the body cannot break it down (ie. coal dust) because it accumulates in the lungs, causes in-elasticity of the lungs, etc. if we are talking about nano-particles of eliquid....well that's the point. Very small droplets of nicotine juice are being deposited in your lungs, and absorbed. I'm sure this is not ideal compared to NOT breathing in vapors, but I also STRONGLY doubt that it is very harmful. And if the metal nanoparticles are from the devices/tanks/cartridges rather than the elquid itself, than just mandate glass interiors to tanks, or some other non-reactive surface, and I think we'll be square.

There's also the accusation that e-ciggs produce formaldehyde. The study which found this was essentially burning e-liquid rather than vaping it, so if used normally and desirably, e-ciggs don't produce that. There's also no incentive to burn your eliquid, as when it happens, it tastes really, really gross. So I don't think there's a danger of people trying to do so:

http://ntr.oxfordjournals.org/content/early/2014/05/14/ntr.ntu078.full

In addition there have been several studies which DO link e-cig use to reduced smoking:

http://www.ecigarette-research.com/web/index.php/2013-04-07-09-50-07/2014/186-ecig-rct http://www.biomedcentral.com/content/pdf/1471-2458-14-1159.pdf http://ntr.oxfordjournals.org/content/early/2014/10/29/ntr.ntu200

Well, safer the cigarettes.

People say that there's no reason to smoke an e-cig unless you're trying to quit smoking cigs, but there's also no reason to ever want to smoke cigarettes, and yet we have booming industries coming from both products.

Honestly, if kids are going to get hooked on something, I think I'm still glad that they're choosing the lesser of two evils, even if it's still shitty for them.

I mean, in your article and in the original article the consensus is that e-cigs are less dangerous, and we see quotes like,

The decline in cigarette use among teenagers accelerated substantially from 2013 to 2014, dropping by 25 percent, the fastest pace in years.

The pattern seemed to go against the dire predictions of anti-tobacco advocates that e-cigarettes would become a gateway to cigarettes among youths, and suggested they might actually be helping, not hurting. The pattern resembled those in Sweden and Norway, where a rise in the use of snus, a smokeless tobacco product, was followed by a sharp decline in cigarette use.

I'm not saying that e-cigs are good, and I definitely don't think people should be using them, but let's not pretend like this isn't better than kids smoking regular cigarettes--unless there's some way to prove that this will lead them onto that, which seems dubious, given, again, that,

“They’re not a gateway in, and they might be accelerating the gateway out,” said David B. Abrams, executive director of the Schroeder Institute for Tobacco Research and Policy Studies, an anti-tobacco group.