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As per Satoshi's "Peer-to-Peer Electronic Cash System": P2P is a 'prerequisite' for the system to 'enable' electronic cash.
It does not work the other way around.
But these spammers dont even care about decentralization, so boring.
The decentralization argument is bogus since it ignores Nielsen's law, Moore's law etc.
http://www.nngroup.com/articles/law-of-bandwidth/ 1MB in 2008 when Bitcoin was first announced is actually equivalent to 17 MB today. (50% compounded per year for 7 years).