Right but that pertains only to undefined witness versions. If you limit the BIP to OP_IF, OP_RETURN and output sizes in current witness versions, there would be no risk of HF or ossification. I understand that cutting off the current avenues for spam would incentivize use of undefined witness versions. But these are restricted by policy in both Core and Knots. If scammers migrate to v2+ we can force Core to take a stronger stand on policy, since they do really want to protect the upgrade hooks currently afforded by it.