Nonhuman animals are sentient beings with the desire to live, and the right to live, just as much as we are. They didn't choose to be born into their species any more than we chose to be born as humans. And even if they had, it wouldn't matter. All sentient beings are equal, regardless of physical body, and simply having the physical ability to exploit, torture, and murder beings of other species does not make doing so morally justifiable. Just as humans don't want to be tortured and murdered, and just as we desire to live full and happy lives, free from oppression, so do all animals. They want nothing from humanity except to be left alone: To be allowed to live full and happy lives, free from human oppression.

Some will argue that humans are superior (usually based on intelligence) and therefore have the right to exploit, torture, and murder beings of 'lesser' species. However, this argument also allows us to exploit, torture, and murder other humans.
Scientists believe that adult pigs have an equal intelligence to that of three year old humans. Therefore, if it is morally acceptable for a human to eat a pig based on intelligence, it is also morally acceptable for an adult human to eat a three year old human child. This argument would also mean that it is morally acceptable for us to eat mentally handicapped humans, many of whom are far less intelligent than the nonhuman animals consumed by humans.
Additionally, this argument allows for beings with superior intelligence to exploit, torture, murder, and consume humans. If an alien race were to invade Earth--a race far more intelligent than humans, just as much as humans are more intelligent than pigs or chickens or cows--they would be justified in enslaving the human race, breeding humans, keeping them in horrible living conditions and subjecting them to torture, and finally slaughtering them and consuming their corpses.
Just as humans do not have the moral right to murder and consume human babies or mentally handicapped humans, and just as intellectually advanced species do not have the right to murder and consume humans, neither do humans have the right to murder and consume nonhuman animals based solely on a lesser intellect.

Some might also argue that humans have 'always' eaten meat, that it is therefore natural for humans to eat meat, and that this justifies the consumption of meat. However, some will also argue that many things now accepted as morally wrong, such as racism, sexism, war, murder, rape, theft, and slavery, are natural simply because humans have done those things for a long time. Whether or not they are wrong, humans can live fulfilling lives without doing these things, and therefore many humans abstain from most or all of these things. These things are abstained from based on morality, not what is natural: If these things are judged based on morality rather than nature, so too should speciesism and the consumption of meat. Innocent, sentient beings are tortured and murdered just to satisfy the tastebuds of humans. Just to satisfy the selfish, greedy desires for personal pleasure and convenience. There is no valid justification for this any more than there is for racism, sexism, or many other things now accepted as morally wrong.
In addition, humans are naturally herbivores. The only animal product which humans are meant to consume is breast milk from our own mothers. Herbivorous humans (Vegans) usually live much healthier lives. Vegans have extremely low rates of cancer, heart disease, brain disease, diabetes, impotence, Alzheimer's, strokes, obesity, and almost every other human health issue.
Not only are humans much healthier as herbivores, but our physical characteristics suggest that we are meant to consume only plants. We don't have large canine teeth capable of tearing through the hide of animals. We don't have claws capable of sinking into animals' bodies and killing them. The only way we are able to consume flesh is through the use of tools and weapons, while we are able to eat fruits and vegetables without any tools or weapons, just as all other species are able to obtain and consume their natural diets without the help of tools or weapons. Not only do humans lack the natural physical capabilities to kill and consume animals, but raw flesh is unappealing to most humans. Humans only consume flesh after it is carefully removed from the carcass of an animal and cooked, not at all like omnivorous and carnivorous species.
We also share many other characteristics of herbivorous species. Our stomach acidity has a pH of less than 1 with food in our stomach, just like herbivorous species. However, both omnivorous and carnivorous species have a pH of over 4 with food in their stomachs. Like herbivores, our saliva contains enzymes which break down carbohydrates, which is lacked by omnivores and carnivores. Our small intestine is 10 to 11 times our body length. Herbivores' small intestine is 10 to 12+ times their body length, while that of omnivores is 4 to 6 times their body length, and that of carnivores is only 3 to 6 times their body length. Like herbivores, our teeth and nails are flat and relatively dull, while omnivores and carnivores have sharp, long, curved claws and teeth.

There are countless reasons to go Vegan. There are no reasons to go on consuming the chopped up corpses of tortured animals. Put innocent, sentient life above your personal desires. Go Vegan.