Any group of miners that has 51+% of the hashpower can impose any rules they are forced to impose. This will be the eventual consequence of losing the ability to run a full node anonymously. Governments will create laws that will dictate which transactions miners are allowed to accept into the blockchain and no-one can go around them because anonymous nodes are not possible anymore.
The bitcoin layer cannot be scaled much above the current levels while keeping it decentralized. There are some who think it’s already scaled too much. The second layers are the only option with the possibility of decentralization.