Unfortunately there are four flaws in your little story. One: Sunlight only causes cancer under certain circumstances as in far too much exposure. Two: Sunlight is natural and inevitable (unlike smoking). Three: Smoking is something that is much easier and reasonable to ban than sunlight. Four: Someone that is resistant to sunlight can take precautions of their own such as sunscreen, an umbrella, etc. as they are a minority (such as smokers are a minority as well).