I had a similar discussion with supertestnet at tabconf, except he argued significantly better than Chris Guida did.

essentially the idea is that they want those transactions off of their system until they HAVE to pull them in (as blocks), because they want to avoid propagating those transactions, regardless of whether they'll end up in blocks or not. the idea is that if enough people run the filters, MAYBE some non-monetary transactions can be prevented.

he obviously acknowledged that you can always go to a miner anyway and include whatever you want, so long as it doesn't break consensus if you really care about it