Satoshi Nakamoto: The total cost of that "spam" is greater than its price in the fee. "The question isn't whether spam can outbid me; the question is the infrastructure cost that spam forces the entire ecosystem to pay. Every transaction, whether spam or an essential payment.

Nick Szabo: And the biggest cost of the spam isn't the volume; it's the legal and moral risks that come with arbitrary non-financial content, which are far larger, far less predictable, and far less manageable by the bitcoin leal community, than the legal and moral risks from merely arbitrary financial transactions.