Yet, many feel that they should be permitted to take hardware the purchased and tinker with it legally. If I were to write some code that allowed me to interact with a cartridge that I bought, why shouldn't I be able to share that code with others that might also wish to tinker with their cartridges in the same manner?

If you make emulation of hardware that doesn't infringe on copyright illegal, you stamp out a lot of legal and useful tinkering.