Smoking should be banned at outdoor restaurants. Not because it would limit the health damage an individual smoker does to themself – there are already numerous public health interventions designed to reduce the harm people are willing to visit upon themselves through smoking (tobacco excise, plain packaging, Quit campaigns).
Instead, the ban is necessary to protect the health of other restaurant patrons, who shouldn’t be forced to inhale second-hand smoke. The ban would also improve the amenity of their meals; by being able to taste their food, rather than nicotine, and not leaving the restaurant reeking of smoke.
But the most important reason to ban smoking in outdoor restaurants is to protect the health of the employees of these venues. They shouldn’t have to cough repeatedly during their work, they shouldn’t go home smelling of tobacco – above all, they shouldn’t be put at risk of cancer because of someone else’s actions.