I thought of something to respond to this with as I was reading, but the damned thing fell out of my brain.

However, I would like to submit that implicitly, through the social contract of being paid for posting here, that all steem content is implicitly thereby public domain, even linked to media objects. This is not to say that attribution can be neglected, in fact it makes it more important. It's really not that much extra effort when you took the other user's material and simply mention their name, at minimum, if not citing the post where it was first placed into the blockchain.