The spam filters literally aren't working currently. If they were... we wouldn't even be talking about this stuff.

It's stored in the witness because it's disguised as program code... and because witness data gets the ~75% discount.

It can be 'ignored' ie not 'computed' (that's my understanding at least) but it cannot be pruned. The nodes ignore anything in op_if op_end (iiuc) but it is still stored.

Op_return outputs can be pruned plus don't bloat the utxo set plus are 4x more expensive for spammers