Because your natural sense of wanting to do the right, responsible and unselfish thing can be appealed to without resort to coercion by the State. It's the same argument I've made with respect to the abortion issue for years.
First of all, laws regulating abortion do not involve coersion in any shape or form. Secondly, your position has consistently been that States do not have the right to reflect the will of the people by formulating their own laws - a position which directly contradicts the Constitution of the United States of America.