His reasoning is wrong. An external fee market will develop among miners with spammers paying a premium over the mempool fee because it can't get relayed any other way. It could actually further decentralize mining because some small 1% miner could charge say a 1% premium vs say Foundry taking a 10% fee. Patient spammers will take it and wait a day for a block. Filtering this way will accelerate spammers running out of money. As with everything in bitcoin, sticking to your principles is the path to victory.