WATCH: Prop. 8 Plaintiffs on the Momentum of Equality

As judge after judge around the nation rules for marriage equality, what's driving the decisions is less about marriage and more about equality, say two of the plaintiffs in the case that brought down California's Proposition 8.

"I believe it's the justices and judges across the land ... they understand that this is the law," said Jeff Zarrillo, appearing Thursday on MSNBC's NOW With Alex Wagner to discuss the new documentary The Case Against 8. "This isn't about whether you're a Republican or a Democrat. This is about being an American, and they're interpreting the law as every person in this country as everyone in this country deserves the same rights, whether you're gay, straight, bisexual, or transgender. Everybody deserves those same rights. So what you're seeing now is states where you never would have expected coming along, with Arkansas and Texas and Utah and states like that. ... Now we're getting the flyover states."

Added his husband, Paul Katami: "This is about marriage for us, the case is about marriage, the film documents this absolutely amazing case, this legal strategy to make sure that Prop. 8 never happens again, but the fact of the matter is ... it's not really about marriage, it's about being treated equally. The big damage here is that we were treated like second-class citizens, and when you talk to any minority group, that's a universal theme. So we say that there should never be a barrier to equality."

Sandy Stier and Kris Perry were plaintiffs in the Prop. 8 case along with Zarrillo and Katami, and both couples, along with lawyers Ted Olson and David Boies, are featured in The Case Against 8. The film will be in theaters beginning June 6, with a release in New York and Los Angeles, and open in other major cities June 13. It will then premiere on HBO June 23. It's been a hit on the film festival circuit and brought filmmakers Ben Cotner and Ryan White the U.S. documentary directing award at Sundance.

Read more about the film here and here, and watch Zarrillo and Katami's conversation with Alex Wagner below.