He, beings capable of interstellar travel would have very little need for "slaves", I mean, even on mean old earth slaves only made sense until 1 coal joule was

He, beings capable of interstellar travel would have very little need for "slaves", I mean, even on mean old earth slaves only made sense until 1 coal joule was cheaper than 1 man joule. If you can travel over light years a joule is going to be extraordinarily cheap, or time is not relevant. Either way, very hard for me to see how human slaves would be of any use to them.