I literally gave an example of an Ordinal-like transaction funding 160-bit addresses, and treating these as chunks of information instead. You will have no way to telling if that is an Ordinal or a regular transaction. And at that point, it's even worse, because full nodes now need to keep worthless UTXO.
If they choose that route and willingly limit the size of the junk they are injecting into the chain to 160 bit (20 bytes) chunks, we've successfully prevented spam. Because that is nowhere near enough for them to create the parallel market to scam people with ergo killing the incentive and halting the spam.
You see, this type of scam only works when they can show the idiots something like the monkey picture on their website or something complicated that the newbies unfamiliar with technical stuff think is actually an "NFT token". That is why they buy into the scam. Otherwise they can not fool them with 20 bytes.
Not to mention OP_RETURN is 4 times bigger and can hold 640 bits (80 bytes)!
BTW right now their junk is also creating dust outputs bloating the UTXO database.