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.
An OP_RETURN output can definitely contain more non-OP information than a standard segwit native transaction, but the problem remains. People can still inject images as chunks of addresses.
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.
Nowhere near it? Lol. We're talking about people who waste thousands of dollars worth of bitcoin for transaction fees, and you think the same cannot repeat if there appears to be enough demand?
That is why they buy into the scam. Otherwise they can not fool them with 20 bytes.
This is another level of speculation. If you can fool people into buying "digital images", I'm pretty sure there will be some dumb asses who will buy the same concept under the "chunks of addresses". It's the same piece of information in the end.
Not to mention OP_RETURN is 4 times bigger and can hold 640 bits (80 bytes)!
They could also split it in 256-bit chunks, as with multi-sig segwit.