Conservative lawmakers want porn taxes. Critics say they’re unconstitutional.

As age-verification laws continue to dismantle the adult industry—and determine the future of free speech on the internet—a Utah lawmaker proposed a bill this week that would enforce a tax on porn sites that operate within the state.

Introduced by state senator Calvin Musselman, a Republican, the bill would impose a 7 percent tax on total receipts “from sales, distributions, memberships, subscriptions, performances, and content amounting to material harmful to minors that is produced, sold...