" long-term human departure from earth would mean that much of the life forms that make human life possible go with us" What, CM? I always imagined an earth without human life would flourish in all its current state and evolve quite nicely.
Anyway, eventually the sun's gonna blow up, so maybe we want to be elsewhere when that happens? I don't think the idea of humans leaving Earth is a bad one, just an unlikely one at this point.
@4 I believe he was musing on how many organisms and what types humans would need to bring with them to sustain human existence in space, not the prospect of removing life forms from Earth.