Humans have the ability to alter the environment around them. Humans are working how they take a freindly environment with them when travelling across space. Humans are working on how they alter the environment, so that is friendly, at the destination.
Where do you get the idea that humans are nutritious? So called "man-eating" sharks often spit-out victims after only one, albeit fatal, bite.
If humans were harvested, we would be aware of frequent unexplainable disappearances of people, large scale unexplanable disappearances of people. These cases would be reported in the traditional media not exclusively on YouTube
I supect your ideas may have come from the Predator franchise, Twilight Zone: To Serve Man or Soylent Green.
You are even ignoring UFO/ETH lore. There is a video floating about that where a man named COLLINS(?) speaks of a "Grey" know as "EBE". (My memory is vague on the details, but I'm sure other readers know it.) Anyway EBE is described as a chlorphyll based life-form; so EBE needed a botanist rather than a physician for healthcare. I would guess this type of "Grey" wouldn't eat humans.
Edited by Mangoze, 17 February 2011 - 11:34 PM.