I didn't read the argument, but i think it must be crap because humanity is a terrible fuel source; especially since the vacuum of space does not prevent machines from using the power of the sun as an energy source more directly that humans. Enslaving humans would be extremely inefficient.
I am really skeptical about all of this... GDP growth creates jobs and more of the citizen can have more stuff... but "citizen happiness" is more psychologically and culturally influenced more than based on a certain standard of living. ... also, this is the worst comment ever...