There are reasonable moral arguments against copyright infringement, but the false equivocation with stealing is not one of them.
The same moral principles that argue against depriving people of natural property they already own do not imply further arguments against reducing sales opportunities for non-rival goods for which scarcity has been artificially established via positive law. Other, unrelated principles, can make for compelling arguments, but not the same ones.
Most people do, since groceries are physical, rival goods to which natural property rights apply. But if it were possible to make copies of groceries while leaving the originals intact, far fewer people would argue against that on the same grounds. They might make other, unrelated arguments against copying, but moral principles applicable to physical property wouldn't be relevant.