Satoshi was against putting “arbitrary data” (such as messages or images) on the Bitcoin chain. His own messages make three ideas clear:

- Do not put clear messages/data on the chain. On the idea of attaching text to payments, he said: “It would not be wise to have plain text messages permanently recorded... it would be an accident waiting to happen.” He proposed that, if messaging were to be included, it should be a separate system from Bitcoin.

- For non-monetary uses (e.g., DNS), another chain is better. In the BitDNS debate, he explained that stacking other systems on top of the Bitcoin chain does not scale and that “Bitcoin and BitDNS can be used separately; users should not have to download both to use one or the other.” He also pointed out that space on the Bitcoin chain is expensive.

- Concern about “bloat.” He anticipated that Bitcoin users could become “increasingly strict” in limiting the size of the chain and keeping it accessible to many devices.

“Re: Suggestion: Allow short messages to be sent together with bitcoins?” — Oct 23, 2010

Key line: “It would be unwise to have permanently recorded plaintext messages… an accident waiting to happen.” — Satoshi rejects storing messages on-chain and says a messaging system should be separate from Bitcoin.

“Re: BitDNS and Generalizing Bitcoin” — Dec 9–10, 2010

“I think it would be possible for BitDNS to be a completely separate network and separate block chain…” — pushes other uses (like DNS) off Bitcoin.

“Piling every proof-of-work quorum system in the world into one dataset doesn’t scale… Users shouldn’t have to download all of both to use one or the other.” — warns against burdening Bitcoin with unrelated data/protocols.

“Re: Version 0.3.18” — Dec 9, 2010

“I… support a third transaction type for timestamp hash-sized arbitrary data… [so] nodes… don’t need to… index it.” — if you must anchor data, keep it hash-only and non-indexed (minimizes bloat).