That to me is the problem with attacking PETA for "insulting" the memory of enslaved African Americans. The Thirteenth Amendment was inspired by their suffering, but it's not about memory. "Shall not exist" is forward looking; to confine its command to history understates our responsibility today. The fight against enslavement and involuntary servitude is far from won. Serious people are trying to apply the Thirteenth Amendment to contemporary problems like human trafficking, exploitation of children, and migrant farm labor. If the Thirteenth Amendment is only about American chattel slavery, then defenders of the status quo can dismiss and ridicule those arguments.

But those critics are correct that for PETA to equate animals with slaves is profoundly reactionary. It's a metaphor, and once let loose it can be damaging. George Fitzhugh, one of the leading apologists for slavery, in 1854 mocked Jefferson's arguments for human equality by writing "men are not 'born entitled to equal rights!' It would be far nearer the truth to say, 'that some were born with saddles on their backs, and others booted and spurred to ride them,' -- and the riding does them good." The Thirteenth Amendment embodied the revolutionary idea that all human beings are human in every significant way -- no saddles, no boots, no connection to the plantation. But animals can't be "equal" to human beings, not because humans are "speciesist" but because the very idea of equality is meaningless in that context. If we begin to analogize animals to slaves at all, we run the risk of sliding back into a very dangerous mode of thought.

At the same time, laughter isn't the answer; the moral aspect of our treatment of animals needs more attention than it gets. PETA is good at grabbing headlines, but often offers people a chance to deflect its genuine concerns by expressing them in gimmicky and distasteful ways. It's hard to take anything about them seriously after their ad displaying Sherlyn Chopra semi-nude with a chain around her ankle and the legend WHIPS AND CHAINS BELONG IN THE BEDROOM, NOT IN THE CIRCUS.

The issue of human-animal relations deserves more seriousness than either side brings to it currently; so does the issue of slavery and freedom in the contemporary world. The answer won't lie in blurring the issues. The simple fact is that animals -- even appealing ones like orcas and dolphins -- can't have legal rights. That's not because of anyone's "original intentions," but because rights imply that their holder has the agency to invoke them (PETA's suit is brought by the orcas' "next friends," who are humans seeking to convince the court to create a special relationship to the animals) and the capacity to follow the obligations that come with them. If humans come to understand and value animals more -- as I hope we will -- it will not be because they have "rights," but because we have more understanding of our place in the world. The way we treat animals is about the way we define ourselves, not about them.

Human equality -- the removal of coercion and exploitation from our daily lives -- is an imperative if we want to live in a truly free and democratic world. Humane treatment of animals is important if we are to realize our own moral natures. Confusing the two -- equating orcas with slaves, for example -- risks diluting both impulses, and turning serious challenges into gimmicks.