But, then again, I'm an avowed speciesist.
What other purpose were animals put on this Earth for? To balance the ecosystem and to provide as you said a benefit for humans. The freaking cheetahs hunt down gazelles to eat and survive. They don't give a **** about the gazelles feelings. Now I don't think you should beat and abuse animals, or electrocute chickens (Reportedly KFC does that).
I thought we had something special!!!
But, most importantly, humanity has advanced to a level where we no longer need to sustain ourselves with animal products. A cheetah has a biological imperative to eat a gazelle, whereas we'll eat a gazelle simply because we may find it tasty. We might hide the gazelle's skin into leather (is that even possible? lol), and wear it as clothes or fashion a couch out of it, but we don't need to.