I skimmed through the whole thread and no one mentioned the potential human beings hold that all other animals lack. Humans are the only ones that have a chance of getting off this planet and colonizing other planets.
This may be a slim chance, but it's infinitely better than no chance at all. We have a chance at spreading life throughout the galaxy. This gives humans a potential universal importance in helping the universe becoming aware of itself.
http://www.space.com/scienceastronom...exoplanet.html
But a billion pigs certainly are not less important than one human simply because a billion pigs can feed millions of humans for a long time.