If you've seen Free Willy, you'll understand the emotional appeal behind PETA's latest lawsuit, but the organization has a spotty history equating human slavery with keeping animals in captivity. In the past, the NAACP has scolded PETA for making this kind of comparison, accusing PETA of having "pimped" African Americans.

The Associated Press explains the SeaWorld case thusly:

People for the Ethical Treatment of Animals is accusing the SeaWorld parks of keeping five star-performer whales in conditions that violate the 13th Amendment ban on slavery. SeaWorld depicted the suit as baseless.

The chances of the suit succeeding are slim, according to legal experts not involved in the case; any judge who hews to the original intent of the authors of the amendment is unlikely to find that they wanted to protect animals. But PETA relishes engaging in the court of public opinion, as evidenced by its provocative anti-fur and pro-vegan campaigns.

The case boils down to PETA trying to win constitutional rights for five orca whales, and the AP says the animal rights organization has had five lawyers working on the case for a year-and-a-half. The commitment is admirable to say the least, but PETA has had a tough time making the case for "animal slavery," even to the people who are most likely to agree with them.

In 2008, the Institute for the Development of Earth Awareness (IDEA) and Marjorie Spiegel, the author of The Dreaded Comparison: Human and Animal Slavery, sued PETA for copyright infringement over a traveling exhibition that featured images of black Americans alongside animals in cages. Spiegel complained that the exhibit meant that readers would "be forced to view it through the distorted prism that PETA has created" and "degrade and impair public discourse." Civil rights groups similarly scolded the organization. "Once again, Black people are being pimped. You used us. You have used us enough," the NAACP complained. A judge eventually threw out the case, and PETA has since continued to draw the comparison between African American slavery and animals in cages. As recently as July of this year, PETA scrambled to defend the reference in another exhibition in Washington DC.

Despite past criticism, PETA's charging ahead with the historical reference. "The historical context is undeniable," Jeff Kerr, a PETA lawyer, told the AP. "But that's not what this case is about. It's about the orcas in their own right, not whether they are or aren't similar to humans."

We've reached out to the NAACP to hear their thoughts on the latest case and will update as soon as we hear back.