From philosopher Steve Sapontzis:
Very briefly, the argument for [animal liberation] runs as follows. Morality is goal-directed activity which aims at making the world a better place in terms of reduced suffering and frustration, increased happiness and fulfilment, a wider reign of fairness and respect for others, and enhanced presence and effectiveness of such virtues as kindness and impartiality. Through our exploitation of nonhuman animals we detract from all of these moral goals. Factory farming, fur trapping and other exploitations of nonhuman animals increase the suffering and frustration in the world and reduce happiness and fulfilment – the exact opposite of our moral goals. In using our vast power over nonhuman animals to make them bear burdens and suffer losses so that we may be comfortable and prosperous, we extend and enforce a reign of tyranny and disregard, verging on contempt, for others – again, the exact opposite of our moral goals. Finally, by giving revulsion at and compassion for the suffering of nonhuman animals the demeaning labels of ‘squeamishness’ and ‘sentimentality’ and by conditioning children to disregard such feelings as they learn to hunt, butcher or vivisect nonhuman animals, we limit and inhibit the virtues of which we are capable — again, just the opposite of our moral goals. Consequently, in all these ways our goal of making the world a morally better place will be more effectively pursued by liberating from human exploitation all those capable of suffering and happiness and of being treated fairly and virtuously.
This extract comes from an article found here.