This argument conflates two separate issues:

1. Relaying unconfirmed transactions

2. Relaying blocks validated by your node.

The first is something you should be able to control and filter as a node runner.

The second you cannot control if you want to be a part of the current network as a node runner.

Saying "filters don't work" is saying you shouldn't control what UNCONFIRMED transaction your node propagates because some other node might send it along to a miner and eventually get included into a block which you HAVE to relay to be part of the network.

Filtering txns makes it less likely that a spam transaction makes it into a block though obviously not impossible.