Don't know personally I'd love to see them get studies asap. If they prove there's still a possibility of second hand damage then yeah treat it the same as smoking. If not then allow it as premises see fit.
There are some good studies going on at the moment. We should know more about the potential hazards later this year (hopefully).
Fact is, though, the stage is already set with desperation from the antis to spin any old factor into a factor for harm. The study that this very thread is based on is little more than a negative spin on something that demonstrated vaping is 99% cleaner than smoking cigarettes. That's fact. Yet instead of that being the headline, the results are published in a negative light.
There are likely more carcinogens in an overcooked steak, quite frankly.
If studies come in showing that vapour has levels of content that are beyond allowed (legal) safe levels in indoor air then yes, absolutely, they should be treated the same as smoking and vapers sent outside.
But the same action shouldn't be taken from a study that shows "there's something in there", but at levels not considered a concern -- yet blown up in the media to be akin to mustard gas.
Beyond that, the rest is an issue of etiquette. As maxilive says, I wouldn't be happy with someone blowing vapour all over me in Subway as I'm eating my lunch. Much the same as I wouldn't be pleased with a random individual walking over and farting on me (and that's not even considering what you're inhaling from their intestinal gas -- maybe the media should jump on that?). Users do need to mindful of their behaviour.
"What? It's nothing; it's legal; it isn't doing you any harm!" isn't an excuse when you're blowing vapour all over people who don't want it. It's perfectly possible to keep your vaping "on the DL" and behave yourself. It isn't like smoke -- it doesn't need to be exhaled in such volume to prevent choking yourself.
No nuisance, no problem, as far as I'm concerned. That goes for both vapers and non-vapers. Just because you see someone putting a PV to their mouth doesn't mean you have license to raise an issue over it.
As soon as they blow it all over you, though... you have every right to ask them to rein it in if it's making you uncomfortable. Same as any other behaviour such as swearing, farting, belching, shouting, fighting... whatever.