Speciesism is wrong because, like racism, sexism, and homophobia, it excludes sentient beings from full membership in the moral community based on an irrelevant characteristic. Race, sex, sexual orientation, and species are all irrelevant to the capacity to be harmed.
But the rejection of speciesism on this ground implies the rejection of discrimination based on race, sex, or sexual orientation. It is unacceptable to perpetuate the commodification of one group for the benefit of another. Commodification involves treating the other—whether a woman, person of color, gay or lesbian, or nonhuman—as an object, as something rather than as someone.
For many years, People for the Ethical Treatment of Animals has promoted sexist campaigns. This started with their “I’d rather go naked than wear fur” campaign in the early 1990s and has degenerated through a series of increasing sexist promotions culminating in its most recent PETA’s State of the Union Undress.