back in the 50s and 60s there was simply no reason not to. It made you cough and was smelly but it wasn't seen as a real risk except by a very few people. On the plus side it was thought to be cool (an image heavily encouraged by ciggy makers).
Look at these: Reagan, John Wayne, "Its He-Man Aroma WOWS the Ladies!", "Not One Single Case of Throat Irritation"
http://gcaggiano.word...ell-were-we-thinking/
I remember Mad Magazine used to run spoof cigarette ads back in the 60s as an anti-smoking campaign; this was very prescient but seen as quite bizarre at the time.