So in short, the primary argument FOR is that they generate passive income for some purported bid bot 'investor'? How exactly is that supposed to scale?
Just like capitalism. You know, the real world.
Someone offers "work" (or "labor") - this is the content creator. Someone else offers "capital" - this is the passive investor.
Labor + capital = prosperity
Except that the steem economy needs diversification. Just "content and attention" (the "blogging business") is not enough.
We now have games too (Steem Monsters - @steemmonsters, Drug Wars @drugwars, Next Colony @nextcolony, etc), but more diversification is needed.
We used to have "open source software" with Utopian but alas, that business folded.
We have Fundition @fundtion for charity management but I'm not sure it's thriving.
I talked for instance about a marketplace for selling art here: Revisiting Steemland: a fairer and more transparent art market as a new "export".
Another idea is a marketplace for selling unused storage space. A bit like filecoin / storj / sia / bittorrent but with the power of the best cryptoeconomic system, that of steem: Steembit: a decentralized storage marketplace for Steemland
There are a bunch of other ideas for diversification, like @oracle-d for instance.
The more diverse the types of work one can source from Steemland (supposedly better quality or cheaper price than elsewhere), the more attractive the ecosystem is for investors.