So a retailer provides a device, and now becomes liable for a fine of $500 for every porn site on the internet that their filter fails to block? That's one hell of a fine.
If this passes - which it may well, because Alabama works hard to maintain its reputation - then it's just going to be tied up in court for years. Once it gets out of that, no retailer in the state is going to be able to risk selling computers, phones or games consoles any more - unless they have the big pockets to defend themselves in court. You'll see a lot more people buying from Amazon - and no Amazon warehouses in Alabama.