If you don’t want people to be able to add arbitrary data in OP_RETURN transactions, you should create a BIP that makes these transactions invalid.
This was already discussed enough when the OP code was introduced back in the days, there is no need to create a BIP. The majority think it is needed and in fact one of the reasons why it was kept is as you guessed:
I would also point out that if OP RETURN transactions could not include data, people would start sending minimum output amounts to vanity addresses that send some kind of message. This would both increase the blockchain size and the UTXO set.