There are many fine frum rabbonim who smoke.
If we’re going to argue that it’s assur to engage in any behavior that can be bad for health, than why not say cholent, nosh, ice cream, kugel and cake are assur? Obesity, high cholesterol, high blood pressure are serious health problems, too.
Second hand smoke is as real as man-made global warming. In other words, it’s a farce that’s been debunked.