Creating an altcoin system which stores its data in blockchain is parasitic and increases the cost for non-consenting Bitcoin uses— and I think that is not great, and, I think it's pretty objectively clear that it bloats the blockchain, but that is not what I was complaining about.

Nor do I think we needed _yet another thread_ to help pump the name of this latest altcoin. This will be my one and only post in this thread and I hope other people decline to help give free PR here by continuing to post in this thread and giving them a free controversy to spin.

The issue here is that that mastercoin stores data in Bitcoin by creating perpetually unredeemable transaction outputs. It doesn't just store data in the blockchain, it stores it in the UTXO set and the blockchain. The former is a more precious resource than the latter. This kind of behavior, if wide spread, changes the asymptotic fast storage requirements for a full validating node from something close to constant (just some growth due to forever lost Bitcoins which all users are paid for via deflation) to perpetually growing.  The ability to for a full node to forget old transaction data would currently let you run one with about 2% of the storage that the blockchain takes up, but these outputs cannot be spent so they cannot be forgotten.

I am reasonably confident that you would prefer I defend Bitcoin by nicely asking as opposed to the alternatives.

No more than the door of your home cares when some thief walks through it when you've left it unlocked.  The technically possibility of something does not equal moral authority, nor does the possibility of doing something now guarantee that that possibility will remain in the future— especially if it causes harm to others, like taking up their resource for private use. Just because it's possible doesn't mean its right, nor does it mean that its wise.

I certainly believe the users of Bitcoin care and will take action to defend Bitcoin from use which is harmful to it. Some time back I'd made a minor technical proposal which would completely block data-storage txouts with no impact to normal Bitcoin usage.  Adopting it would require switching people to a new address style for new transactions, so it's not something that would be adopted quickly if the Bitcoin userbase were to decide to go down that route, but it certainly could be done.  I tend to think asking nicely is preferable, however.

I have better things to do with my time than to provide free consulting for altcoins who've just raised hundreds of thousands of dollars worth of investments in their ill considered schemes. The concerns here are not new, the impacts of unspendable outputs are not mysterous to people who have even half a technical clue about the Bitcoin system, and the solutions are not subtle.

My preference is that you do what hundreds of other altcoins have done and not store your data inside Bitcoin (but feel free to merge-mine if you need a consensus system), don't non-consensually consume the resources of people who are disinterested— even opposed— to your system... but failing that, see what all the other people piling on are saying about keeping data out of the UTXO set as a bare minimum.