removing the filtering entirely unifies the network, where some nodes and miners didn't see entire classes of valid transactions.

unification of the network is important when considering potential issue that lead to forks or attacks that cause forks on purpose.

removing the right to configure this is also a consideration towards this end. We don't want people to self segregate. Division among nodes when that division is not consensus is not good. It doesn't help anything. It doesn't stop the spam. It just divides us up and the spam causes more issues elsewhere, not on your node today but on all nodes tomorrow (UTXO bloat)