Since we, as a society, understand how horrible these sorts of sufferings are, we try to protect humans from those who might kill, mutilate, or cage them, regardless of the benefits to others that such sufferings might bring. Animals whom we have made our slaves, we do not like to consider our equals. Based on common physiology and behavior, it is safe to say that vertebrate animals suffer fear when their lives are threatened, pain when their bodies are mutilated, and boredom and frustration when caged for long periods of time. For those who can suffer, the degree of suffering, not the species of the sufferer, is what should count. Similarly, if an individual desires to live, then its life should be respected.
Animals show they value their lives and freedom by their struggles against being caged and killed.
The act of depriving them of life or freedom harms them in many of the same ways a human is harmed when deprived of life or freedom. Right, a longer essay on animal rights, is available as part of our Vegan Advocacy booklet.