Yes. If they want to ban smoking in public places, such as airports they can. However they should not be able to dictate to business such as bars and resturants. If it is not illegal then it is up to the business. If you think smoking pot does not cause cancer you need to do more research.
NIDA - Research Report Series - Marijuana Abuse
Cancer of the respiratory tract and lungs may also be promoted by marijuana smoke.4 A study comparing 173 cancer patients and 176 healthy individuals produced strong evidence that smoking marijuana increases the likelihood of developing cancer of the head or neck, and that the more marijuana smoked, the greater the increase.17 A statistical analysis of the data suggested that marijuana smoking doubled or tripled the risk of these cancers.
Marijuana has the potential to promote cancer of the lungs and other parts of the respiratory tract because it contains irritants and carcinogens.40 In fact, marijuana smoke contains 50 percent to 70 percent more carcinogenic hydrocarbons than does tobacco smoke.41 It also produces high levels of an enzyme that converts certain hydrocarbons into their carcinogenic form, levels that may accelerate the changes that ultimately produce malignant cells.
42 Marijuana users usually inhale more deeply and hold their breath longer than tobacco smokers do, which increases the lungs' exposure to carcinogenic smoke. These facts suggest that, puff for puff, smoking marijuana may increase the risk of cancer more than smoking tobacco does.