>big corporations start using LLMs to learn how to lock things down even further

Why would they? They just need to fund lobbyist to make it illegal for any AI to reverse engineer anything copyrighted or with IP.

Sure, you can use open source AI to do it but not everyone will/can do it.

So, they don't need to ban everyone, they just need to make sure the final code isn't available freely on GitHub. That would minimize the damage, it's not a perfect solution but more than enough to protect the company.