If we use Satoshi's words as argument, we probably should use his comment about BitDNS project as well[1].
That comment refers to BitDNS as being a separate network and having its own blockchain instead of residing on Bitcoin's blockchain. He is proposing a merge mining scheme, where finding a Bitcoin block would entail also finding a block on BitDNS' blockchain using the same Proof of Work.
That's right. But my point is satoshi suggesting to store arbitrary data on different network, while OP's idea store arbitrary data on Bitcoin on-chain network. That could be used as argument against storing arbitary data on-chain.