What I have heard before is: - more resource-efficient and green since livestock farming requires a lot of feed and has a higher carbon footprint than all vehicles combined, and - that it's less cruel than raising animals to be slaughtered.
In terms of economics, a cheaper meat substitute would just mean a cheaper source of protein for people, comparable to eating vegetables.
As a side note, does anyone know why Paul Graham has been talking about economic inequality recently? Is it just politics season and that this is a debate issue?