The issue of course is that you cannot stop arbitrary data and op_return was put in place to provide a printable place to put arbitrary data vs having it pollute the utxo set. Locking down the system to remove all vectors of injecting data would remove nearly all functionality of Bitcoin beyond the most basic uses and doom the scalability of the system. It will be freedom money for the few and relegate it to the same fate of the gold standard if it even makes it that far. The best way to make sure bitcoin is used as money and not arbitrary data is to use it as money.