People do it, and I don't think there is any law against it, but it's all down to stigma, I'm sure if people complained or didn't know what it was they could ask you to stop.
I vape in the back room of work, my boss asked me to go outside the first time but i just blew some near him and he said mmm it doesn't smell and he let me stay inside Same goes for airport i'd say your guna get pulled up but if your polite and explain it they should be ok with it, but yea your guna get some dirty looks from uninformed people i'd say.
But the people who have the guts to do it are guna further the cause the most, I myself would be too nervous to vape in a public place Think of all the smokers that would see you and go wow hes smoking inside and security let him do it, i'm guna find out what that is and buy one