I've heard this talking point before, which is the whole thing that saddens me, I'm not against people wanting to run knots, but stupid repition of talking points like these make it seem like a psyop.
Anyways to reply, It's more like putting a lock on an open door, plus it corrupts incentives OP_RETURN is meant for data we can safely ignore doing stupid stuff like this incentives jpeggers to bloat the UTXO set, which is much worse.