It's never been my position that we have a right to kill animals indiscriminately because we are smarter/stronger/more advanced than they are, even if that principle plays itself out on in nature every day (remember the lion killing the gazelle for food?). Your response to that scenario is that the lion doesn't have any choice but the kill the gazelle (or antelope or zebra, etc...) for food and therefore the ethics of it don't come into question, but we do. My position is that when it comes down to it, we also have no choice unless we are willing to drastically reduce the numbers of our own species to accomodate that position so that vegetarianism is possible for everyone on the planet and in that situation would have a viable choice to eat animals or not.
Who knows, with advanced technology, it may someday be possible to produce a cheap complete protein source that is non-animal in origin in sufficient quantity to supply the entire population. Until such time, though, we're still stuck with the necessity of needing both plants and animals to live and we need both to ensure that as many people as possible have sufficient food to survive.
After all, a person who is starving or who has starving children doesn't want to debate the ethics of whether or not he should kill an animal to eat...their survival and the survival of their children is more important to them at that point than the life of an animal. Maybe it shouldn't be that way, but I have yet to meet a person who would be willing to starve or allow their children to starve to avoid killing an animal when the death of that animal would prevent it.