If only smoking harmed just the user, but secondhand smoke kills children daily in the US. https://www.lung.org/quit-smoking/smoking-facts/health-effects/secondhand-smoke

It's also been found that 3rd-hand smoke can be just as dangerous a secondhand smoke. Not to mention that smoking smells awful and makes indoor and outdoor public places unpleasant. Smokers also routinely fail to dispose of cigarettes properly, leading to unsightly and unhealthy toxic litter, and causes multiple uncontrolled forest/wildfires every year.

You need to throw out your preconceived notions about smoking and the purpose of laws, they are not compatible with reality.