I have no opinion on this, and I'm not ashamed to admit I've no idea what the Mastercoin argument is, do you think you could spare a sentence or two as to why you think it's spam Luke, and perhaps the other guy as to why he doesn't think it's spam? Just something short and sweet to inform the rest of us, not a lengthy troll or anything.
tl;dr: People using Bitcoin have all agreed to store financial data and nothing else, using a scripting system to convey it. But MasterCoin transactions include metadata and unnecessary bloat, and lie about what kind of data it is in a way that makes the entire Bitcoin network less efficient.
From my understanding of MasterCoin, there are two ways I, and probably anyone who considers the blockchain to have a social agreement/contract, consider it spam:
1) The unnecessary 1Exodus output indicating it is a Mastercoin transaction.
2) The abuse of multisig and p2pkh outputs to convey data rather than OP_RETURN.
3) Some of the data may be non-financial/transactional in nature.
Basically anything that isn't a pubkey shouldn't be scripted as a pubkey, anything that isn't a hash shouldn't be scripted as a hash, and anything that isn't financial data (not sure if this exists, but it was implied in this conversation earlier that it did) shouldn't appear directly in the blockchain.
There is also an argument that MasterCoin is competing in supply (one cannot convert more bitcoins to mastercoins or vice-versa) and many users may not wish to support it when they store/validate the blockchain. Note I don't hold to this argument myself, as it seems to logically rule out any use of the blockchain for things like smart property (note that S.P. does in fact not require using the blockchain at all, but if it did, I don't see how it would violate the social contract of Bitcoin).
Not per se related to spam, I think it would also be ideal if Mastercoin migrated to its own blockchain - it really has no inherent need to be inside bitcoin's, and does not benefit from being there either. It does benefit from having bitcoin miners securing it, but that can also be had by supporting some form of merged mining, which is just as safe if those same miners freely support it.
I am arguing here more from the point of Counterparty (XCP) than Mastercoin (MSC) here, because I know more about Counterparty and I am more heavily invested in it. (And I do have some issues with the way Mastercoin was founded/funded and some aspects of its implementation, and I have no such issues with Counterparty.) However, I believe that Mastercoin supporters could generally use these same arguments.
Personally, I question the "social agreement/contract" aspect. To me, the software/code is the entirety of the contract. That is kind of the whole point of a decentralized, trustless, electronic currency. The rules are stated in the code, and enforced by the code. Any transaction that meets the rules of the Bitcoin code is a valid Bitcoin transaction, by definition.
On the other hand, I do see the validity to the argument that each "miner" has the right to mine only the transactions that he sees fit. However, I do not think that "pool operator" necessarily equates to "miner" and I would be interested to see a poll or something among Eligius miners asking whether or not they support including XCP and MSC transactions in Eligius-mined blocks. Not to do so is leaving money on the table, and miners are notoriously ROI-minded. AFAIK Counterparty is pretty generous with the fees, given the transaction sizes. (Annoyingly so, as an XCP user.) (And I am aware of Eligius' support of GBT and promotion of its use, which would skirt this issue entirely as well as ensure continued decentralization for Bitcoin. Now if only we could get people to actually use it...)
Now, to address your points specifically:
1) I do think that the use of the Exodus address is dumb, wasteful, and leads to the unjust enrichment of the Mastercoin developers. This is not an issue with Counterparty.
2) As long as the multisig outputs fit the coded definition of valid Bitcoin transactions, they are valid Bitcoin transactions.
3) While it is possible to encode pure data / in a Counterparty transaction, it is meaningless and requires a fee. It would be the same as if I sent .0000001BTC to address "1HiLukeJrXXXXXXXXXXXXxxxx" using the Bitcoin reference QT client. The vast majority of Counterparty transactions are indeed financial / transactional in nature. That is the whole point of Counterparty.
"Basically anything that isn't a pubkey shouldn't be scripted as a pubkey, anything that isn't a hash shouldn't be scripted as a hash, and anything that isn't financial data (not sure if this exists, but it was implied in this conversation earlier that it did) shouldn't appear directly in the blockchain."
How can you tell whether something is or isn't a pubkey? How can you tell whether something is or isn't a hash? And again, aside from the small occurrence of true spam (for which the same potential exists in plain-jane Bitcoin), all Counterparty transactions are indeed transactional and financial in nature. And the Counterparty developers would certainly prefer for *everything* (except for valid escrow/m-of-n situations) to take place in OP_RETURN instead of being encoded in pubkeys or anywhere else.
As for moving to a merged-mined separate chain, the number of XCP tokens never increases. It is impossible to create them; they are fixed in number, and to change this would basically destroy Counterparty. Counterparty transaction fees are paid in BTC (except for asset issuance, which requires XCP to be burned forever). Counterparty users must periodically buy BTC if they make a lot of Counterparty transactions. There could therefore be no reward for miners in a Counterparty-only blockchain.
Lastly, I have to close with this. As a supporter of Bitcoin, wouldn't you rather have this functionality (decentralized exchange; like a stock market for crypto-currencies and crypto-assets) exist on the Bitcoin blockchain and be a part of the Bitcoin ecosystem instead of having all of this functionality take place in NXT, BTSX, Ethereum, Ripple, etc. and leave Bitcoin in the dust as a simple/stupid currency-only? Does the idea of this not excite you? Think about displacing ALL of the corrupt stock exchanges in the world, with something provably fair and honest and decentralized! This is what is going to happen, and what Counterparty and Mastercoin are trying to make happen on the Bitcoin blockchain, with Bitcoin as the common price denominator. Wouldn't you rather be able to buy a share of Overstock directly with BTC instead of NXT, and to have that transaction immortalized in the Bitcoin blockchain instead of the NXT blockchain? Wouldn't you like to see on the ticker "Shares of Overstock are trading at .05 BTC today" instead of USD, NXT, or some other currency? Woudn't that strengthen and accelerate the growth and acceptance of Bitcoin to an incredible degree? It's coming. One way or another, it's coming. Overstock is already in discussions with multiple crypto-asset projects, including Counterparty. As a Bitcoin supporter, would you rather this future be "Built on Bitcoin" or built on something else?
Honestly it amazes me to hear you suggest that any project should be "on their own blockchain". What, and derail the work and the value that has been put into Bitcoin? To someday possibly eclipse Bitcoin? Of course as a Bitcoin developer, you can't go crazy and implement every weird idea that's come up in every altcoin out there (not that there are that many good ideas in the altcoin world). Can't rock the boat too much, and you don't want to put anything untested into production. Stability is definitely the core concern at this point. But adding new features and value to Bitcoin should also be a priority, and if third-parties are able to do this discretely and "on top of" Bitcoin without disturbing Bitcoin-per-se in any significant way, I think they should be encouraged.