You can’t stop pubkey spam. Publey spam bloats the utxo set. Bloating the utxo set makes it impossible to run a node on minimal hardware because ram requirements become to great. This is already happening today. An better analogy is. There is a porch shitter who shits on your doormat everyday. You can’t stop them so you put a bucket out to hope that they will have the decency to use it. Welcome to the decentralized permissionless world.