In order to make the application and enforcement of this act uniform throughout the state, it is the intent of the legislature to preempt, to the exclusion of city and county governments, the regulation of the sale, loan, distribution, dissemination, presentation or exhibition to a minor of material which is obscene or which is harmful to minors and depicts in whole or in part nudity, sexual conduct or sado-masochistic abuse. To that end, it is hereby declared that every city or county ordinance adopted before the effective date of this act which deals with the regulation of the sale, loan, distribution, dissemination, presentation or exhibition to a minor of material which is obscene or which is harmful to minors and depicts in whole or in part nudity, sexual conduct or sado-masochistic abuse, shall stand abrogated and unenforceable on or after such effective date; and that no city or county government shall have the power to adopt any ordinance relating to the regulation of the sale, loan, distribution, dissemination, presentation or exhibition to a minor of material which is obscene or which is harmful to minors and depicts in whole or in part nudity, sexual conduct or sado-masochistic abuse, on or after such effective date.